Just In Time

Java 1.7 New Features Over 1.6

2012-06-08T18:45:00.002-07:00

Automatic Resource Management

Description: A proposal to support scoping of resource usage in a block with automatic resource cleanup. This addresses the common and messy problem of correctly closing or releasing resources in a finally block, particularly when needing to close multiple resources in the same block.

this:

BufferedReader br = new BufferedReader(new FileReader(path));
try {
return br.readLine();
} finally {
br.close();
}

becomes:

try (BufferedReader br = new BufferedReader(new FileReader(path)) {
return br.readLine();
}

// Start a block using two resources, which will automatically
// be cleaned up when the block exits scope
do (BufferedInputStream bis = …; BufferedOutputStream bos = …) {
… // Perform action with bis and bos
}

You can declare more than one resource to close:

try (
InputStream in = new FileInputStream(src);
OutputStream out = new FileOutputStream(dest))
{
// code
}

Underscores in numeric literals

int one_million = 1_000_000;

Strings in switch

String s = ...
switch(s) {
case "quux":
processQuux(s);
// fall-through
case "foo":
case "bar":
processFooOrBar(s);
break;
case "baz":
processBaz(s);
// fall-through
default:
processDefault(s);
break;
}

Binary literals

int binary = 0b1001_1001;

Improved Type Inference for Generic Instance Creation

Map<String, List<String>> anagrams = new HashMap<String, List<String>>();

become:

Map<String, List<String>> anagrams = new HashMap<>();

Better exception handling

this:

} catch (FirstException ex) {
logger.error(ex);
throw ex;
} catch (SecondException ex) {
logger.error(ex);
throw ex;
}

become:

} catch (FirstException | SecondException ex) {
logger.error(ex);
throw ex;
}

Language level XML support

Description: Add support for multi-line XML (or possibly other languages or kinds of text) to be embedded within code.

Example:

elt.appendChild(
<muppet>
<name>Kermit</name>
</muppet>);

Big Decimal operator support

Description: Add support for manipulating BigDecimal objects with arithmetic operators (just like other numeric primitives) instead of via method calls.

Enhanced null handling

Description: Null-ignore invocation is concerned with dealing with possible null values in calling one or especially a chain of methods.

For example, instead of

public String getPostcode(Person person) {
if (person != null) {
Address address = person.getAddress();
if (address != null) {
return address.getPostcode();
}
}
return null;
}

you could instead call:

public String getPostcode(Person person) {
return person?.getAddress()?.getPostcode();
}

New file system API (NIO 2.0)

File change notifications -> The WatchService API lets you receive notification events upon changes to the subject (directory or file).

The steps involved in implementing the API are:

Create a WatchService. This service consists of a queue to hold WatchKeys.
Register the directory/file you wish to monitor with this WatchService.
While registering, specify the types of events you wish to receive (create, modify or delete events)
You have to start an infinite loop to listen to events
When an event occurs, a WatchKey is placed into the queue
Consume the WatchKey and invoke queries on it.

Date and Time API

Description: This JSR will provide a new and improved date and time API for Java. The main goal is to build upon the lessons learned from the first two APIs (Date and Calendar) in Java SE, providing a more advanced and comprehensive model for date and time manipulation.
The new API will be targeted at all applications needing a data model for dates and times. This model will go beyond classes to replace Date and Calendar, to include representations of date without time, time without date, durations and intervals. This will raise the quality of application code. For example, instead of using an int to store a duration, and javadoc to describe it as being a number of days, the date and time model will provide a class defining it unambiguously.

Read Gmail from Java

2011-11-23T10:02:00.000-08:00

package com.timers;

import java.util.Properties;

import javax.mail.Flags;
import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.NoSuchProviderException;
import javax.mail.Session;
import javax.mail.Store;
import javax.mail.search.FlagTerm;
/**
*
* @author Vinay Guntaka
* mail.jar is required to execute this program (download from java2s.com)
* And your Gmail Credentails.
* This Program reads only unread mails of your box
*
*/
public class ReadGmail {
    public static void main(String args[]) {
        while (true) {
            try {
                System.out.println("Started.......");
                Start();
                System.out.println("...Read completed.......");

                try {
                    Thread.sleep(1000 * 5);
                } catch (InterruptedException e1) {

                }

            } catch (Exception e) {

                try {
                    e.printStackTrace();
                    System.out.println("..Error in connection Sleeping...");

                } catch (Exception e1) {

                }
            }
        }

    }

    public static void Start() throws Exception {
        Properties props = System.getProperties();

        props.setProperty("mail.store.protocol", "imaps");
        try {
            Session session = Session.getDefaultInstance(props, null);
            Store store = session.getStore("imaps");
            //simply username dnt include @gmail.com
            store.connect("imap.gmail.com", "username", "password");
            System.out.println(store);
            int cout = 0;

            Folder inbox = store.getFolder("Inbox");
            inbox.open(Folder.READ_ONLY);

            // / to read only unread mails
            FlagTerm ft = new FlagTerm(new Flags(Flags.Flag.SEEN), false);
            Message messages[] = inbox.search(ft);

            // To read all mails from inbox
            //Message messages[] = inbox.getMessages();

            for (Message message : messages) {
                System.out.println("Reading:" + (messages.length - cout));
                System.out.println("MEssage Content :: --"
                        + message.getSubject() + message.getReceivedDate());
                cout++;
            }

        } catch (NoSuchProviderException e) {
            e.printStackTrace();

        } catch (MessagingException e) {
            e.printStackTrace();

        }

    }
}

Hibernate

2011-10-30T11:44:00.000-07:00

1.What is ORM ?

ORM stands for object/relational mapping. ORM is the automated persistence of objects in a Java application to the tables in a relational database.

2.What does ORM consists of ?

An ORM solution consists of the followig four pieces:

API for performing basic CRUD operations
API to express queries refering to classes
Facilities to specify metadata
Optimization facilities : dirty checking,lazy associations fetching

3.What are the ORM levels ?

The ORM levels are:

Pure relational (stored procedure.)
Light objects mapping (JDBC)
Medium object mapping
Full object Mapping (composition,inheritance, polymorphism, persistence by reachability)

4.What is Hibernate?

Hibernate is a pure Java object-relational mapping (ORM) and persistence framework that allows you to map plain old Java objects to relational database tables using (XML) configuration files.Its purpose is to relieve the developer from a significant amount of relational data persistence-related programming tasks.

5.Why do you need ORM tools like hibernate?

The main advantage of ORM like hibernate is that it shields developers from messy SQL. Apart from this, ORM provides following benefits:

Improved productivity
- High-level object-oriented API
- Less Java code to write
- No SQL to write
Improved performance
- Sophisticated caching
- Lazy loading
- Eager loading
Improved maintainability
- A lot less code to write
Improved portability
- ORM framework generates database-specific SQL for you

6.What Does Hibernate Simplify?

Hibernate simplifies:

Saving and retrieving your domain objects
Making database column and table name changes
Centralizing pre save and post retrieve logic
Complex joins for retrieving related items
Schema creation from object model

7.What is the need for Hibernate xml mapping file?

Hibernate mapping file tells Hibernate which tables and columns to use to load and store objects. Typical mapping file look as follows:

8.What are the most common methods of Hibernate configuration?

The most common methods of Hibernate configuration are:

Programmatic configuration
XML configuration (hibernate.cfg.xml)

9.What are the important tags of hibernate.cfg.xml?

Following are the important tags of hibernate.cfg.xml:

10.What are the Core interfaces are of Hibernate framework?

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The five core interfaces are used in just about every Hibernate application. Using these interfaces, you can store and retrieve persistent objects and control transactions.

Session interface
SessionFactory interface
Configuration interface
Transaction interface
Query and Criteria interfaces

11.What role does the Session interface play in Hibernate?

The Session interface is the primary interface used by Hibernate applications. It is a single-threaded, short-lived object representing a conversation between the application and the persistent store. It allows you to create query objects to retrieve persistent objects.
Session session = sessionFactory.openSession();

Session interface role:

Wraps a JDBC connection
Factory for Transaction
Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier

12.What role does the SessionFactory interface play in Hibernate?

The application obtains Session instances from a SessionFactory. There is typically a single SessionFactory for the whole application—created during application initialization. The SessionFactory caches generate SQL statements and other mapping metadata that Hibernate uses at runtime. It also holds cached data that has been read in one unit of work and may be reused in a future unit of work
SessionFactory sessionFactory = configuration.buildSessionFactory();

13.What is the general flow of Hibernate communication with RDBMS?

The general flow of Hibernate communication with RDBMS is :

Load the Hibernate configuration file and create configuration object. It will automatically load all hbm mapping files
Create session factory from configuration object
Get one session from this session factory
Create HQL Query
Execute query to get list containing Java objects

14.What is Hibernate Query Language (HQL)?

Hibernate offers a query language that embodies a very powerful and flexible mechanism to query, store, update, and retrieve objects from a database. This language, the Hibernate query Language (HQL), is an object-oriented extension to SQL.

15.How do you map Java Objects with Database tables?

First we need to write Java domain objects (beans with setter and getter).
Write hbm.xml, where we map java class to table and database columns to Java class variables.

Example :

<hibernate-mapping>
<class name="com.test.User" table="user">
   <property column="USER_NAME" length="255"
      name="userName" not-null="true" type="java.lang.String"/>
   <property column="USER_PASSWORD" length="255"
name="userPassword" not-null="true" type="java.lang.String"/>
</class>
</hibernate-mapping>

16.What’s the difference between load() and get()?

load() vs. get() :-

load()	get()
Only use the load() method if you are sure that the object exists.	If you are not sure that the object exists, then use one of the get() methods.
load() method will throw an exception if the unique id is not found in the database.	get() method will return null if the unique id is not found in the database.
load() just returns a proxy by default and database won’t be hit until the proxy is first invoked.	get() will hit the database immediately.

17.What is the difference between and merge and update ?

Use update() if you are sure that the session does not contain an already persistent instance with the same identifier, and merge() if you want to merge your modifications at any time without consideration of the state of the session.

18.How do you define sequence generated primary key in hibernate?

Using <generator> tag.Example:-

<id column="USER_ID" name="id" type="java.lang.Long">
<generator class="sequence">
<param name="table">SEQUENCE_NAME</param>
<generator>
</id>

19.Define cascade and inverse option in one-many mapping?

cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"

inverse - mark this collection as the "inverse" end of a bidirectional association.
inverse="true|false"
Essentially "inverse" indicates which end of a relationship should be ignored, so when persisting a parent who has a collection of children, should you ask the parent for its list of children, or ask the children who the parents are?

20.What do you mean by Named – SQL query?

Named SQL queries are defined in the mapping xml document and called wherever required.Example:

<sql-query name = "empdetails">
   <return alias="emp" class="com.test.Employee"/>
    SELECT emp.EMP_ID AS {emp.empid},
                 emp.EMP_ADDRESS AS {emp.address},
                 emp.EMP_NAME AS {emp.name}
FROM Employee EMP WHERE emp.NAME LIKE :name
</sql-query>

Invoke Named Query :

List people = session.getNamedQuery("empdetails")
.setString("TomBrady", name)
.setMaxResults(50)
.list();

21.How do you invoke Stored Procedures?

<sql-query name="selectAllEmployees_SP" callable="true">
<return alias="emp" class="employee">
<return-property name="empid" column="EMP_ID"/>

<return-property name="name" column="EMP_NAME"/>
<return-property name="address" column="EMP_ADDRESS"/>
{ ? = call selectAllEmployees() } </return>
</sql-query>

22.Explain Criteria API

Criteria is a simplified API for retrieving entities by composing Criterion objects. This is a very convenient approach for functionality like "search" screens where there is a variable number of conditions to be placed upon the result set.Example :

List employees = session.createCriteria(Employee.class)
.add(Restrictions.like("name", "a%") )
.add(Restrictions.like("address", "Boston"))
.addOrder(Order.asc("name") )
.list();

23.Define HibernateTemplate?

org.springframework.orm.hibernate.HibernateTemplate is a helper class which provides different methods for querying/retrieving data from the database. It also converts checked HibernateExceptions into unchecked DataAccessExceptions.

24.What are the benefits does HibernateTemplate provide?

The benefits of HibernateTemplate are :

HibernateTemplate, a Spring Template class simplifies interactions with Hibernate Session.
Common functions are simplified to single method calls.
Sessions are automatically closed.
Exceptions are automatically caught and converted to runtime exceptions.

25.How do you switch between relational databases without code changes?

Using Hibernate SQL Dialects , we can switch databases. Hibernate will generate appropriate hql queries based on the dialect defined.

26.If you want to see the Hibernate generated SQL statements on console, what should we do?

In Hibernate configuration file set as follows: <property name="show_sql">true</property>

27.What are derived properties?

The properties that are not mapped to a column, but calculated at runtime by evaluation of an expression are called derived properties. The expression can be defined using the formula attribute of the element.

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28.What is component mapping in Hibernate?

A component is an object saved as a value, not as a reference
A component can be saved directly without needing to declare interfaces or identifier properties
Required to define an empty constructor
Shared references not supported

Example:

29.What is the difference between sorted and ordered collection in hibernate?

sorted collection vs. order collection :-

sorted collection	order collection
A sorted collection is sorting a collection by utilizing the sorting features provided by the Java collections framework. The sorting occurs in the memory of JVM which running Hibernate, after the data being read from database using java comparator.	Order collection is sorting a collection by specifying the order-by clause for sorting this collection when retrieval.
If your collection is not large, it will be more efficient way to sort it.	If your collection is very large, it will be more efficient way to sort it .

31.What is the advantage of Hibernate over jdbc?

Hibernate Vs. JDBC :-

JDBC	Hibernate
With JDBC, developer has to write code to map an object model's data representation to a relational data model and its corresponding database schema.	Hibernate is flexible and powerful ORM solution to map Java classes to database tables. Hibernate itself takes care of this mapping using XML files so developer does not need to write code for this.
With JDBC, the automatic mapping of Java objects with database tables and vice versa conversion is to be taken care of by the developer manually with lines of code.	Hibernate provides transparent persistence and developer does not need to write code explicitly to map database tables tuples to application objects during interaction with RDBMS.
JDBC supports only native Structured Query Language (SQL). Developer has to find out the efficient way to access database, i.e. to select effective query from a number of queries to perform same task.	Hibernate provides a powerful query language Hibernate Query Language (independent from type of database) that is expressed in a familiar SQL like syntax and includes full support for polymorphic queries. Hibernate also supports native SQL statements. It also selects an effective way to perform a database manipulation task for an application.
Application using JDBC to handle persistent data (database tables) having database specific code in large amount. The code written to map table data to application objects and vice versa is actually to map table fields to object properties. As table changed or database changed then it’s essential to change object structure as well as to change code written to map table-to-object/object-to-table.	Hibernate provides this mapping itself. The actual mapping between tables and application objects is done in XML files. If there is change in Database or in any table then the only need to change XML file properties.
With JDBC, it is developer’s responsibility to handle JDBC result set and convert it to Java objects through code to use this persistent data in application. So with JDBC, mapping between Java objects and database tables is done manually.	Hibernate reduces lines of code by maintaining object-table mapping itself and returns result to application in form of Java objects. It relieves programmer from manual handling of persistent data, hence reducing the development time and maintenance cost.
With JDBC, caching is maintained by hand-coding.	Hibernate, with Transparent Persistence, cache is set to application work space. Relational tuples are moved to this cache as a result of query. It improves performance if client application reads same data many times for same write. Automatic Transparent Persistence allows the developer to concentrate more on business logic rather than this application code.
In JDBC there is no check that always every user has updated data. This check has to be added by the developer.	Hibernate enables developer to define version type field to application, due to this defined field Hibernate updates version field of database table every time relational tuple is updated in form of Java class object to that table. So if two users retrieve same tuple and then modify it and one user save this modified tuple to database, version is automatically updated for this tuple by Hibernate. When other user tries to save updated tuple to database then it does not allow saving it because this user does not have updated data.

32.What are the Collection types in Hibernate ?

Bag
Set
List
Array
Map

33.What are the ways to express joins in HQL?

HQL provides four ways of expressing (inner and outer) joins:-

An implicit association join
An ordinary join in the FROM clause
A fetch join in the FROM clause.
A theta-style join in the WHERE clause.

34.Define cascade and inverse option in one-many mapping?

35.What is Hibernate proxy?

The proxy attribute enables lazy initialization of persistent instances of the class. Hibernate will initially return CGLIB proxies which implement the named interface. The actual persistent object will be loaded when a method of the proxy is invoked.

36.How can Hibernate be configured to access an instance variable directly and not through a setter method ?

By mapping the property with access="field" in Hibernate metadata. This forces hibernate to bypass the setter method and access the instance variable directly while initializing a newly loaded object.

37.How can a whole class be mapped as immutable?

Mark the class as mutable="false" (Default is true),. This specifies that instances of the class are (not) mutable. Immutable classes, may not be updated or deleted by the application.

38.What is the use of dynamic-insert and dynamic-update attributes in a class mapping?

dynamic-update (defaults to false): Specifies that UPDATE SQL should be generated at runtime and contain only those columns whose values have changed
dynamic-insert (defaults to false): Specifies that INSERT SQL should be generated at runtime and contain only the columns whose values are not null.

39.What do you mean by fetching strategy ?

A fetching strategy is the strategy Hibernate will use for retrieving associated objects if the application needs to navigate the association. Fetch strategies may be declared in the O/R mapping metadata, or over-ridden by a particular HQL or Criteria query.

40.What is automatic dirty checking?

Automatic dirty checking is a feature that saves us the effort of explicitly asking Hibernate to update the database when we modify the state of an object inside a transaction.

41.What is transactional write-behind?

Hibernate uses a sophisticated algorithm to determine an efficient ordering that avoids database foreign key constraint violations but is still sufficiently predictable to the user. This feature is called transactional write-behind.

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42.What are Callback interfaces?

Callback interfaces allow the application to receive a notification when something interesting happens to an object—for example, when an object is loaded, saved, or deleted. Hibernate applications don't need to implement these callbacks, but they're useful for implementing certain kinds of generic functionality.

43.What are the types of Hibernate instance states ?

Three types of instance states:

Transient -The instance is not associated with any persistence context
Persistent -The instance is associated with a persistence context
Detached -The instance was associated with a persistence context which has been closed – currently not associated

44.What are the differences between EJB 3.0 & Hibernate

Hibernate Vs EJB 3.0 :-

Hibernate	EJB 3.0
Session–Cache or collection of loaded objects relating to a single unit of work	Persistence Context-Set of entities that can be managed by a given EntityManager is defined by a persistence unit
XDoclet Annotations used to support Attribute Oriented Programming	Java 5.0 Annotations used to support Attribute Oriented Programming
Defines HQL for expressing queries to the database	Defines EJB QL for expressing queries
Supports Entity Relationships through mapping files and annotations in JavaDoc	Support Entity Relationships through Java 5.0 annotations
Provides a Persistence Manager API exposed via the Session, Query, Criteria, and Transaction API	Provides and Entity Manager Interface for managing CRUD operations for an Entity
Provides callback support through lifecycle, interceptor, and validatable interfaces	Provides callback support through Entity Listener and Callback methods
Entity Relationships are unidirectional. Bidirectional relationships are implemented by two unidirectional relationships	Entity Relationships are bidirectional or unidirectional

45.What are the types of inheritance models in Hibernate?

There are three types of inheritance models in Hibernate:

Table per class hierarchy
Table per subclass
Table per concrete class

Q. How will you configure Hibernate?
Answer:

The configuration files hibernate.cfg.xml (or hibernate.properties) and mapping files *.hbm.xml are used by the Configuration class to create (i.e. configure and bootstrap hibernate) the SessionFactory, which in turn creates the Session instances. Session instances are the primary interface for the persistence service.

" hibernate.cfg.xml (alternatively can use hibernate.properties): These two files are used to configure the hibernate sevice (connection driver class, connection URL, connection username, connection password, dialect etc). If both files are present in the classpath then hibernate.cfg.xml file overrides the settings found in the hibernate.properties file.

" Mapping files (*.hbm.xml): These files are used to map persistent objects to a relational database. It is the best practice to store each object in an individual mapping file (i.e mapping file per class) because storing large number of persistent classes into one mapping file can be difficult to manage and maintain. The naming convention is to use the same name as the persistent (POJO) class name. For example Account.class will have a mapping file named Account.hbm.xml. Alternatively hibernate annotations can be used as part of your persistent class code instead of the *.hbm.xml files.

Q. What is a SessionFactory? Is it a thread-safe object?
Answer:

SessionFactory is Hibernates concept of a single datastore and is threadsafe so that many threads can access it concurrently and request for sessions and immutable cache of compiled mappings for a single database. A SessionFactory is usually only built once at startup. SessionFactory should be wrapped in some kind of singleton so that it can be easily accessed in an application code.

SessionFactory sessionFactory = new Configuration().configure().buildSessionfactory();

Q. What is a Session? Can you share a session object between different theads?
Answer:

Session is a light weight and a non-threadsafe object (No, you cannot share it between threads) that represents a single unit-of-work with the database. Sessions are opened by a SessionFactory and then are closed when all work is complete. Session is the primary interface for the persistence service. A session obtains a database connection lazily (i.e. only when required). To avoid creating too many sessions ThreadLocal class can be used as shown below to get the current session no matter how many times you make call to the currentSession() method.

&
public class HibernateUtil {
&
public static final ThreadLocal local = new ThreadLocal();

public static Session currentSession() throws HibernateException {
Session session = (Session) local.get();
//open a new session if this thread has no session
if(session == null) {
session = sessionFactory.openSession();
local.set(session);
}
return session;
}
}

It is also vital that you close your session after your unit of work completes. Note: Keep your Hibernate Session API handy.

Q. What are the benefits of detached objects?
Answer:

Detached objects can be passed across layers all the way up to the presentation layer without having to use any DTOs (Data Transfer Objects). You can later on re-attach the detached objects to another session.
Q. What are the pros and cons of detached objects?
Answer:
Pros:

" When long transactions are required due to user think-time, it is the best practice to break the long transaction up into two or more transactions. You can use detached objects from the first transaction to carry data all the way up to the presentation layer. These detached objects get modified outside a transaction and later on re-attached to a new transaction via another session.

Cons

" In general, working with detached objects is quite cumbersome, and better to not clutter up the session with them if possible. It is better to discard them and re-fetch them on subsequent requests. This approach is not only more portable but also more efficient because - the objects hang around in Hibernate's cache anyway.

" Also from pure rich domain driven design perspective it is recommended to use DTOs (DataTransferObjects) and DOs (DomainObjects) to maintain the separation between Service and UI tiers.

Q. How does Hibernate distinguish between transient (i.e. newly instantiated) and detached objects?
Answer

" Hibernate uses the version property, if there is one.
" If not uses the identifier value. No identifier value means a new object. This does work only for Hibernate managed surrogate keys. Does not work for natural keys and assigned (i.e. not managed by Hibernate) surrogate keys.
" Write your own strategy with Interceptor.isUnsaved().

Q. What is the difference between the session.get() method and the session.load() method?

Both the session.get(..) and session.load() methods create a persistent object by loading the required object from the database. But if there was not such object in the database then the method session.load(..) throws an exception whereas session.get(&) returns null.

Q. What is the difference between the session.update() method and the session.lock() method?

Both of these methods and saveOrUpdate() method are intended for reattaching a detached object. The session.lock() method simply reattaches the object to the session without checking or updating the database on the assumption that the database in sync with the detached object. It is the best practice to use either session.update(..) or session.saveOrUpdate(). Use session.lock() only if you are absolutely sure that the detached object is in sync with your detached object or if it does not matter because you will be overwriting all the columns that would have changed later on within the same transaction.
Note: When you reattach detached objects you need to make sure that the dependent objects are reatched as well.
Q. How would you reatach detached objects to a session when the same object has already been loaded into the session?

You can use the session.merge() method call.

Q. What are the general considerations or best practices for defining your Hibernate persistent classes?

1.You must have a default no-argument constructor for your persistent classes and there should be getXXX() (i.e accessor/getter) and setXXX( i.e. mutator/setter) methods for all your persistable instance variables.

2.You should implement the equals() and hashCode() methods based on your business key and it is important not to use the id field in your equals() and hashCode() definition if the id field is a surrogate key (i.e. Hibernate managed identifier). This is because the Hibernate only generates and sets the field when saving the object.

3. It is recommended to implement the Serializable interface. This is potentially useful if you want to migrate around a multi-processor cluster.

4.The persistent class should not be final because if it is final then lazy loading cannot be used by creating proxy objects.

5.Use XDoclet tags for generating your *.hbm.xml files or Annotations (JDK 1.5 onwards), which are less verbose than *.hbm.xml files.

Core Java

2011-10-30T11:36:00.000-07:00

1.What are the principle concepts of OOPS?

There are four principle concepts upon which object oriented design and programming rest. They are:

Abstraction
Polymorphism
Inheritance
Encapsulation (i.e. easily remembered as A-PIE).

2.What is Abstraction?

Abstraction refers to the act of representing essential features without including the background details or explanations.

3.What is Encapsulation?

Encapsulation is a technique used for hiding the properties and behaviors of an object and allowing outside access only as appropriate. It prevents other objects from directly altering or accessing the properties or methods of the encapsulated object.

4.What is the difference between abstraction and encapsulation?

Abstraction focuses on the outside view of an object (i.e. the interface) Encapsulation (information hiding) prevents clients from seeing it’s inside view, where the behavior of the abstraction is implemented.
Abstraction solves the problem in the design side while Encapsulation is the Implementation.
Encapsulation is the deliverables of Abstraction. Encapsulation barely talks about grouping up your abstraction to suit the developer needs.

5.What is Inheritance?

Inheritance is the process by which objects of one class acquire the properties of objects of another class.
A class that is inherited is called a superclass.
The class that does the inheriting is called a subclass.
Inheritance is done by using the keyword extends.
The two most common reasons to use inheritance are:
- To promote code reuse
- To use polymorphism

6.What is Polymorphism?

Polymorphism is briefly described as "one interface, many implementations." Polymorphism is a characteristic of being able to assign a different meaning or usage to something in different contexts - specifically, to allow an entity such as a variable, a function, or an object to have more than one form.

7.How does Java implement polymorphism?

(Inheritance, Overloading and Overriding are used to achieve Polymorphism in java).
Polymorphism manifests itself in Java in the form of multiple methods having the same name.

In some cases, multiple methods have the same name, but different formal argument lists (overloaded methods).
In other cases, multiple methods have the same name, same return type, and same formal argument list (overridden methods).

8.Explain the different forms of Polymorphism.

There are two types of polymorphism one is Compile time polymorphism and the other is run time polymorphism. Compile time polymorphism is method overloading. Runtime time polymorphism is done using inheritance and interface.Note: From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java:

Method overloading
Method overriding through inheritance
Method overriding through the Java interface

9.What is runtime polymorphism or dynamic method dispatch?

In Java, runtime polymorphism or dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile-time. In this process, an overridden method is called through the reference variable of a superclass. The determination of the method to be called is based on the object being referred to by the reference variable.

10.What is Dynamic Binding?

Binding refers to the linking of a procedure call to the code to be executed in response to the call. Dynamic binding (also known as late binding) means that the code associated with a given procedure call is not known until the time of the call at run-time. It is associated with polymorphism and inheritance.

11.What is method overloading?

Method Overloading means to have two or more methods with same name in the same class with different arguments. The benefit of method overloading is that it allows you to implement methods that support the same semantic operation but differ by argument number or type.Note:

Overloaded methods MUST change the argument list
Overloaded methods CAN change the return type
Overloaded methods CAN change the access modifier
Overloaded methods CAN declare new or broader checked exceptions
A method can be overloaded in the same class or in a subclass

12.What is method overriding?

Method overriding occurs when sub class declares a method that has the same type arguments as a method declared by one of its superclass. The key benefit of overriding is the ability to define behavior that’s specific to a particular subclass type.Note:

The overriding method cannot have a more restrictive access modifier than the method being overridden (Ex: You can’t override a method marked public and make it protected).
You cannot override a method marked final
You cannot override a method marked static

13.What are the differences between method overloading and method overriding?

	Overloaded Method	Overridden Method
Arguments	Must change	Must not change
Return type	Can change	Can’t change except for covariant returns
Exceptions	Can change	Can reduce or eliminate. Must not throw new or broader checked exceptions
Access	Can change	Must not make more restrictive (can be less restrictive)
Invocation	Reference type determines which overloaded version is selected. Happens at compile time.	Object type determines which method is selected. Happens at runtime.

14.Can overloaded methods be override too?

Yes, derived classes still can override the overloaded methods. Polymorphism can still happen. Compiler will not binding the method calls since it is overloaded, because it might be overridden now or in the future.

15.Is it possible to override the main method?

NO, because main is a static method. A static method can't be overridden in Java.

16.How to invoke a superclass version of an Overridden method?

To invoke a superclass method that has been overridden in a subclass, you must either call the method directly through a superclass instance, or use the super prefix in the subclass itself. From the point of the view of the subclass, the super prefix provides an explicit reference to the superclass' implementation of the method.

// From subclass

super.overriddenMethod();

17.What is super?

super is a keyword which is used to access the method or member variables from the superclass. If a method hides one of the member variables in its superclass, the method can refer to the hidden variable through the use of the super keyword. In the same way, if a method overrides one of the methods in its superclass, the method can invoke the overridden method through the use of the super keyword. Note: You can only go back one level. In the constructor, if you use super(), it must be the very first code, and you cannot access any this.xxx variables or methods to compute its parameters.

18.How do you prevent a method from being overridden?

To prevent a specific method from being overridden in a subclass, use the final modifier on the method declaration, which means "this is the final implementation of this method", the end of its inheritance hierarchy.

                       public final void exampleMethod() {
                      // Method statements
                        }

19.What is an Interface?

An interface is a description of a set of methods that conforming implementing classes must have.Note: You can’t mark an interface as final. Interface variables must be static. An Interface cannot extend anything but another interfaces.

20.Can we instantiate an interface?

You can’t instantiate an interface directly, but you can instantiate a class that implements an interface.

21.Can we create an object for an interface?

Yes, it is always necessary to create an object implementation for an interface. Interfaces cannot be instantiated in their own right, so you must write a class that implements the interface and fulfill all the methods defined in it.

22.Do interfaces have member variables?

Interfaces may have member variables, but these are implicitly public, static, and final- in other words, interfaces can declare only constants, not instance variables that are available to all implementations and may be used as key references for method arguments for example.

23.What modifiers are allowed for methods in an Interface?

Only public and abstract modifiers are allowed for methods in interfaces.

24.What is a marker interface?

Marker interfaces are those which do not declare any required methods, but signify their compatibility with certain operations. The java.io.Serializable interface and Cloneable are typical marker interfaces. These do not contain any methods, but classes must implement this interface in order to be serialized and de-serialized.

25.What is an abstract class?

Abstract classes are classes that contain one or more abstract methods. An abstract method is a method that is declared, but contains no implementation. Note:

If even a single method is abstract, the whole class must be declared abstract.
Abstract classes may not be instantiated, and require subclasses to provide implementations for the abstract methods.
You can’t mark a class as both abstract and final.

26.Can we instantiate an abstract class?

An abstract class can never be instantiated. Its sole purpose is to be extended (subclassed).

27.What are the differences between Interface and Abstract class?

Abstract Class	Interfaces
An abstract class can provide complete, default code and/or just the details that have to be overridden.	An interface cannot provide any code at all,just the signature.
In case of abstract class, a class may extend only one abstract class.	A Class may implement several interfaces.
An abstract class can have non-abstract methods.	All methods of an Interface are abstract.
An abstract class can have instance variables.	An Interface cannot have instance variables.
An abstract class can have any visibility: public, private, protected.	An Interface visibility must be public (or) none.
If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly.	If we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method.
An abstract class can contain constructors .	An Interface cannot contain constructors .
Abstract classes are fast.	Interfaces are slow as it requires extra indirection to find corresponding method in the actual class.

28.When should I use abstract classes and when should I use interfaces?

Use Interfaces when…

You see that something in your design will change frequently.
If various implementations only share method signatures then it is better to use Interfaces.
you need some classes to use some methods which you don't want to be included in the class, then you go for the interface, which makes it easy to just implement and make use of the methods defined in the interface.

Use Abstract Class when…

If various implementations are of the same kind and use common behavior or status then abstract class is better to use.
When you want to provide a generalized form of abstraction and leave the implementation task with the inheriting subclass.
Abstract classes are an excellent way to create planned inheritance hierarchies. They're also a good choice for nonleaf classes in class hierarchies.

29.When you declare a method as abstract, can other nonabstract methods access it?

Yes, other nonabstract methods can access a method that you declare as abstract.

30.Can there be an abstract class with no abstract methods in it?

Yes, there can be an abstract class without abstract methods.

31.What is Constructor?

A constructor is a special method whose task is to initialize the object of its class.
It is special because its name is the same as the class name.
They do not have return types, not even void and therefore they cannot return values.
They cannot be inherited, though a derived class can call the base class constructor.
Constructor is invoked whenever an object of its associated class is created.

32.How does the Java default constructor be provided?

If a class defined by the code does not have any constructor, compiler will automatically provide one no-parameter-constructor (default-constructor) for the class in the byte code. The access modifier (public/private/etc.) of the default constructor is the same as the class itself.

33.Can constructor be inherited?

No, constructor cannot be inherited, though a derived class can call the base class constructor.

34.What are the differences between Contructors and Methods?

	Constructors	Methods
Purpose	Create an instance of a class	Group Java statements
Modifiers	Cannot be abstract, final, native, static, or synchronized	Can be abstract, final, native, static, or synchronized
Return Type	No return type, not even void	void or a valid return type
Name	Same name as the class (first letter is capitalized by convention) -- usually a noun	Any name except the class. Method names begin with a lowercase letter by convention -- usually the name of an action
this	Refers to another constructor in the same class. If used, it must be the first line of the constructor	Refers to an instance of the owning class. Cannot be used by static methods.
super	Calls the constructor of the parent class. If used, must be the first line of the constructor	Calls an overridden method in the parent class
Inheritance	Constructors are not inherited	Methods are inherited

35.How are this() and super() used with constructors?

Constructors use this to refer to another constructor in the same class with a different parameter list.
Constructors use super to invoke the superclass's constructor. If a constructor uses super, it must use it in the first line; otherwise, the compiler will complain.

36.What are the differences between Class Methods and Instance Methods?

Class Methods	Instance Methods
Class methods are methods which are declared as static. The method can be called without creating an instance of the class	Instance methods on the other hand require an instance of the class to exist before they can be called, so an instance of a class needs to be created by using the new keyword. Instance methods operate on specific instances of classes.
Class methods can only operate on class members and not on instance members as class methods are unaware of instance members.	Instance methods of the class can also not be called from within a class method unless they are being called on an instance of that class.
Class methods are methods which are declared as static. The method can be called without creating an instance of the class.	Instance methods are not declared as static.

37.How are this() and super() used with constructors?

Constructors use this to refer to another constructor in the same class with a different parameter list.
Constructors use super to invoke the superclass's constructor. If a constructor uses super, it must use it in the first line; otherwise, the compiler will complain.

38.What are Access Specifiers?

One of the techniques in object-oriented programming is encapsulation. It concerns the hiding of data in a class and making this class available only through methods. Java allows you to control access to classes, methods, and fields via so-called access specifiers..

39.What are Access Specifiers available in Java?

Java offers four access specifiers, listed below in decreasing accessibility:

Public- public classes, methods, and fields can be accessed from everywhere.
Protected- protected methods and fields can only be accessed within the same class to which the methods and fields belong, within its subclasses, and within classes of the same package.
Default(no specifier)- If you do not set access to specific level, then such a class, method, or field will be accessible from inside the same package to which the class, method, or field belongs, but not from outside this package.
Private- private methods and fields can only be accessed within the same class to which the methods and fields belong. private methods and fields are not visible within subclasses and are not inherited by subclasses.

Situation	public	protected	default	private
Accessible to class from same package?	yes	yes	yes	no
Accessible to class from different package?	yes	no, unless it is a subclass	no	no

40.What is final modifier?

The final modifier keyword makes that the programmer cannot change the value anymore. The actual meaning depends on whether it is applied to a class, a variable, or a method.

final Classes- A final class cannot have subclasses.
final Variables- A final variable cannot be changed once it is initialized.
final Methods- A final method cannot be overridden by subclasses.

41.What are the uses of final method?

There are two reasons for marking a method as final:

Disallowing subclasses to change the meaning of the method.
Increasing efficiency by allowing the compiler to turn calls to the method into inline Java code.

42.What is static block?

Static block which exactly executed exactly once when the class is first loaded into JVM. Before going to the main method the static block will execute.

43.What are static variables?

Variables that have only one copy per class are known as static variables. They are not attached to a particular instance of a class but rather belong to a class as a whole. They are declared by using the static keyword as a modifier.

static type varIdentifier;

where, the name of the variable is varIdentifier and its data type is specified by type.Note: Static variables that are not explicitly initialized in the code are automatically initialized with a default value. The default value depends on the data type of the variables.

44.What is the difference between static and non-static variables?

A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.

45.What are static methods?

Methods declared with the keyword static as modifier are called static methods or class methods. They are so called because they affect a class as a whole, not a particular instance of the class. Static methods are always invoked without reference to a particular instance of a class.Note:The use of a static method suffers from the following restrictions:

A static method can only call other static methods.
A static method must only access static data.
A static method cannot reference to the current object using keywords super or this.

46.What is an Iterator ?

The Iterator interface is used to step through the elements of a Collection.
Iterators let you process each element of a Collection.
Iterators are a generic way to go through all the elements of a Collection no matter how it is organized.
Iterator is an Interface implemented a different way for every Collection.

47.How do you traverse through a collection using its Iterator?

To use an iterator to traverse through the contents of a collection, follow these steps:

Obtain an iterator to the start of the collection by calling the collectionâ€™s iterator() method.
Set up a loop that makes a call to hasNext(). Have the loop iterate as long as hasNext() returns true.
Within the loop, obtain each element by calling next().

48.How do you remove elements during Iteration?

Iterator also has a method remove() when remove is called, the current element in the iteration is deleted.

49.What is the difference between Enumeration and Iterator?

Enumeration	Iterator
Enumeration doesn't have a remove() method	Iterator has a remove() method
Enumeration acts as Read-only interface, because it has the methods only to traverse and fetch the objects	Can be abstract, final, native, static, or synchronized

Note: So Enumeration is used whenever we want to make Collection objects as Read-only.

50.How is ListIterator?

ListIterator is just like Iterator, except it allows us to access the collection in either the forward or backward direction and lets us modify an element

51.What is the List interface?

The List interface provides support for ordered collections of objects.
Lists may contain duplicate elements.

52.What are the main implementations of the List interface ?

The main implementations of the List interface are as follows :

ArrayList : Resizable-array implementation of the List interface. The best all-around implementation of the List interface.
Vector : Synchronized resizable-array implementation of the List interface with additional "legacy methods."
LinkedList : Doubly-linked list implementation of the List interface. May provide better performance than the ArrayList implementation if elements are frequently inserted or deleted within the list. Useful for queues and double-ended queues (deques).

53.What are the advantages of ArrayList over arrays ?

Some of the advantages ArrayList has over arrays are:

It can grow dynamically
It provides more powerful insertion and search mechanisms than arrays.

54.Difference between ArrayList and Vector ?

ArrayList	Vector
ArrayList is NOT synchronized by default.	Vector List is synchronized by default.
ArrayList can use only Iterator to access the elements.	Vector list can use Iterator and Enumeration Interface to access the elements.
The ArrayList increases its array size by 50 percent if it runs out of room.	A Vector defaults to doubling the size of its array if it runs out of room
ArrayList has no default size.	While vector has a default size of 10.

55.How to obtain Array from an ArrayList ?

Array can be obtained from an ArrayList using toArray() method on ArrayList.

List arrayList = new ArrayList();
arrayList.add(â€¦

ObjectÂ a[] = arrayList.toArray();

56.Why insertion and deletion in ArrayList is slow compared to LinkedList ?

ArrayList internally uses and array to store the elements, when that array gets filled by inserting elements a new array of roughly 1.5 times the size of the original array is created and all the data of old array is copied to new array.
During deletion, all elements present in the array after the deleted elements have to be moved one step back to fill the space created by deletion. In linked list data is stored in nodes that have reference to the previous node and the next node so adding element is simple as creating the node an updating the next pointer on the last node and the previous pointer on the new node. Deletion in linked list is fast because it involves only updating the next pointer in the node before the deleted node and updating the previous pointer in the node after the deleted node.

57.Why are Iterators returned by ArrayList called Fail Fast ?

Because, if list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

58.How do you decide when to use ArrayList and When to use LinkedList?

If you need to support random access, without inserting or removing elements from any place other than the end, then ArrayList offers the optimal collection. If, however, you need to frequently add and remove elements from the middle of the list and only access the list elements sequentially, then LinkedList offers the better implementation.

59.What is the Set interface ?

The Set interface provides methods for accessing the elements of a finite mathematical set
Sets do not allow duplicate elements
Contains no methods other than those inherited from Collection
It adds the restriction that duplicate elements are prohibited
Two Set objects are equal if they contain the same elements

60.What are the main Implementations of the Set interface ?

The main implementations of the List interface are as follows:

HashSet
TreeSet
LinkedHashSet
EnumSet

61.What is a HashSet ?

A HashSet is an unsorted, unordered Set.
It uses the hashcode of the object being inserted (so the more efficient your hashcode() implementation the better access performance you’ll get).
Use this class when you want a collection with no duplicates and you don’t care about order when you iterate through it.

62.What is a TreeSet ?

TreeSet is a Set implementation that keeps the elements in sorted order. The elements are sorted according to the natural order of elements or by the comparator provided at creation time.

63.What is an EnumSet ?

An EnumSet is a specialized set for use with enum types, all of the elements in the EnumSet type that is specified, explicitly or implicitly, when the set is created.

64.Difference between HashSet and TreeSet ?

HashSet	TreeSet
HashSet is under set interface i.e. it does not guarantee for either sorted order or sequence order.	TreeSet is under set i.e. it provides elements in a sorted order (acceding order).
We can add any type of elements to hash set.	We can add only similar types of elements to tree set.

65.What is a Map ?

A map is an object that stores associations between keys and values (key/value pairs).
Given a key, you can find its value. Both keys and values are objects.
The keys must be unique, but the values may be duplicated.
Some maps can accept a null key and null values, others cannot.

66.What are the main Implementations of the Map interface ?

The main implementations of the List interface are as follows:

HashMap
HashTable
TreeMap
EnumMap

67.What is a TreeMap ?

TreeMap actually implements the SortedMap interface which extends the Map interface. In a TreeMap the data will be sorted in ascending order of keys according to the natural order for the key's class, or by the comparator provided at creation time. TreeMap is based on the Red-Black tree data structure.

68.How do you decide when to use HashMap and when to use TreeMap ?

For inserting, deleting, and locating elements in a Map, the HashMap offers the best alternative. If, however, you need to traverse the keys in a sorted order, then TreeMap is your better alternative. Depending upon the size of your collection, it may be faster to add elements to a HashMap, then convert the map to a TreeMap for sorted key traversal.

69.Difference between HashMap and Hashtable ?

HashMap	Hashtable
HashMap lets you have null values as well as one null key.	HashTable does not allows null values as key and value.
The iterator in the HashMap is fail-safe (If you change the map while iterating, you’ll know).	The enumerator for the Hashtable is not fail-safe.
HashMap is unsynchronized.	Hashtable is synchronized.

Note: Only one NULL is allowed as a key in HashMap. HashMap does not allow multiple keys to be NULL. Nevertheless, it can have multiple NULL values.

70.How does a Hashtable internally maintain the key-value pairs?

71.What Are the different Collection Views That Maps Provide?

Maps Provide Three Collection Views.

Key Set - allow a map's contents to be viewed as a set of keys.
Values Collection - allow a map's contents to be viewed as a set of values.
Entry Set - allow a map's contents to be viewed as a set of key-value mappings.

72.What is a KeySet View ?

KeySet is a set returned by the keySet() method of the Map Interface, It is a set that contains all the keys present in the Map.

73.What is a Values Collection View ?

Values Collection View is a collection returned by the values() method of the Map Interface, It contains all the objects present as values in the map.

74.What is an EntrySet View ?

Entry Set view is a set that is returned by the entrySet() method in the map and contains Objects of type Map. Entry each of which has both Key and Value.

75.How do you sort an ArrayList (or any list) of user-defined objects ?

Create an implementation of the java.lang.Comparable interface that knows how to order your objects and pass it to java.util.Collections.sort(List, Comparator).

76.What is the Comparable interface ?

The Comparable interface is used to sort collections and arrays of objects using the Collections.sort() and java.utils.Arrays.sort() methods respectively. The objects of the class implementing the Comparable interface can be ordered.

The Comparable interface in the generic form is written as follows:

interface Comparable<T>

where T is the name of the type parameter.

All classes implementing the Comparable interface must implement the compareTo() method that has the return type as an integer. The signature of the compareTo() method is as follows:

int i = object1.compareTo(object2)

If object1 < object2: The value of i returned will be negative.
If object1 > object2: The value of i returned will be positive.
If object1 = object2: The value of i returned will be zero.

77.What are the differences between the Comparable and Comparator interfaces ?

Comparable	Comparato
It uses the compareTo() method. int objectOne.compareTo(objectTwo).	t uses the compare() method. int compare(ObjOne, ObjTwo)
It is necessary to modify the class whose instance is going to be sorted.	A separate class can be created in order to sort the instances.
Only one sort sequence can be created.	Many sort sequences can be created.
It is frequently used by the API classes.	It used by third-party classes to sort instances.

Exceptions

1.What is an exception?

An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program's instructions.

2.What is error?

An Error indicates that a non-recoverable condition has occurred that should not be caught. Error, a subclass of Throwable, is intended for drastic problems, such as OutOfMemoryError, which would be reported by the JVM itself.

3.Which is superclass of Exception?

"Throwable", the parent class of all exception related classes.

4.What are the advantages of using exception handling?

Exception handling provides the following advantages over "traditional" error management techniques:

Separating Error Handling Code from "Regular" Code.
Propagating Errors Up the Call Stack.
Grouping Error Types and Error Differentiation.

5.What are the types of Exceptions in Java

There are two types of exceptions in Java, unchecked exceptions and checked exceptions.

Checked exceptions: A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses. Each method must either handle all checked exceptions by supplying a catch clause or list each unhandled checked exception as a thrown exception.
Unchecked exceptions: All Exceptions that extend the RuntimeException class are unchecked exceptions. Class Error and its subclasses also are unchecked.

6.Why Errors are Not Checked?

A unchecked exception classes which are the error classes (Error and its subclasses) are exempted from compile-time checking because they can occur at many points in the program and recovery from them is difficult or impossible. A program declaring such exceptions would be pointlessly.

7.Why Runtime Exceptions are Not Checked?

The runtime exception classes (RuntimeException and its subclasses) are exempted from compile-time checking because, in the judgment of the designers of the Java programming language, having to declare such exceptions would not aid significantly in establishing the correctness of programs. Many of the operations and constructs of the Java programming language can result in runtime exceptions. The information available to a compiler, and the level of analysis the compiler performs, are usually not sufficient to establish that such run-time exceptions cannot occur, even though this may be obvious to the programmer. Requiring such exception classes to be declared would simply be an irritation to programmers.

8.Explain the significance of try-catch blocks?

Whenever the exception occurs in Java, we need a way to tell the JVM what code to execute. To do this, we use the try and catch keywords. The try is used to define a block of code in which exceptions may occur. One or more catch clauses match a specific exception to a block of code that handles it.

9.What is the use of finally block?

The finally block encloses code that is always executed at some point after the try block, whether an exception was thrown or not. This is right place to close files, release your network sockets, connections, and perform any other cleanup your code requires.

Note: If the try block executes with no exceptions, the finally block is executed immediately after the try block completes. It there was an exception thrown, the finally block executes immediately after the proper catch block completes

10.What if there is a break or return statement in try block followed by finally block?

If there is a return statement in the try block, the finally block executes right after the return statement encountered, and before the return executes.

11.Can we have the try block without catch block?

Yes, we can have the try block without catch block, but finally block should follow the try block.Note: It is not valid to use a try clause without either a catch clause or a finally clause.

12.What is the difference throw and throws?

throws: Used in a method's signature if a method is capable of causing an exception that it does not handle, so that callers of the method can guard themselves against that exception. If a method is declared as throwing a particular class of exceptions, then any other method that calls it must either have a try-catch clause to handle that exception or must be declared to throw that exception (or its superclass) itself.

A method that does not handle an exception it throws has to announce this:

public void myfunc(int arg) throws MyException {
…
}

throw: Used to trigger an exception. The exception will be caught by the nearest try-catch clause that can catch that type of exception. The flow of execution stops immediately after the throw statement; any subsequent statements are not executed.

To throw an user-defined exception within a block, we use the throw command:

throw new MyException("I always wanted to throw an exception!");

13.How to create custom exceptions?

A. By extending the Exception class or one of its subclasses.

Example:

class MyException extends Exception {
public MyException() { super(); }
public MyException(String s) { super(s); }
}

14.What are the different ways to handle exceptions?

There are two ways to handle exceptions:

Wrapping the desired code in a try block followed by a catch block to catch the exceptions.
List the desired exceptions in the throws clause of the method and let the caller of the method handle those exceptions.

JDBC

1.What is the JDBC?

Java Database Connectivity (JDBC) is a standard Java API to interact with relational databases form Java. JDBC has set of classes and interfaces which can use from Java application and talk to database without learning RDBMS details and using Database Specific JDBC Drivers.

2.What are the new features added to JDBC 4.0?

The major features added in JDBC 4.0 include :

Auto-loading of JDBC driver class
Connection management enhancements
Support for RowId SQL type
DataSet implementation of SQL using Annotations
SQL exception handling enhancements
SQL XML support

3.Explain Basic Steps in writing a Java program using JDBC?

JDBC makes the interaction with RDBMS simple and intuitive. When a Java application needs to access database :

Load the RDBMS specific JDBC driver because this driver actually communicates with the database (Incase of JDBC 4.0 this is automatically loaded).
Open the connection to database which is then used to send SQL statements and get results back.
Create JDBC Statement object. This object contains SQL query.
Execute statement which returns resultset(s). ResultSet contains the tuples of database table as a result of SQL query.
Process the result set.
Close the connection.

4.Exaplain the JDBC Architecture.

The JDBC Architecture consists of two layers:

The JDBC API, which provides the application-to-JDBC Manager connection.
The JDBC Driver API, which supports the JDBC Manager-to-Driver Connection.

The JDBC API uses a driver manager and database-specific drivers to provide transparent connectivity to heterogeneous databases. The JDBC driver manager ensures that the correct driver is used to access each data source. The driver manager is capable of supporting multiple concurrent drivers connected to multiple heterogeneous databases. The location of the driver manager with respect to the JDBC drivers and the Java application is shown in Figure 1.

Figure 1: JDBC Architecture

5.What are the main components of JDBC ?

The life cycle of a servlet consists of the following phases:

DriverManager: Manages a list of database drivers. Matches connection requests from the java application with the proper database driver using communication subprotocol. The first driver that recognizes a certain subprotocol under JDBC will be used to establish a database Connection.
Driver: The database communications link, handling all communication with the database. Normally, once the driver is loaded, the developer need not call it explicitly.
Connection : Interface with all methods for contacting a database.The connection object represents communication context, i.e., all communication with database is through connection object only.
Statement : Encapsulates an SQL statement which is passed to the database to be parsed, compiled, planned and executed.
ResultSet: The ResultSet represents set of rows retrieved due to query execution.

6.How the JDBC application works?

A JDBC application can be logically divided into two layers:

1. Driver layer

2. Application layer

Driver layer consists of DriverManager class and the available JDBC drivers.
The application begins with requesting the DriverManager for the connection.
An appropriate driver is choosen and is used for establishing the connection. This connection is given to the application which falls under the application layer.
The application uses this connection to create Statement kind of objects, through which SQL commands are sent to backend and obtain the results.

Figure 2: JDBC Application

7.How do I load a database driver with JDBC 4.0 / Java 6?

Provided the JAR file containing the driver is properly configured, just place the JAR file in the classpath. Java developers NO longer need to explicitly load JDBC drivers using code like Class.forName() to register a JDBC driver.The DriverManager class takes care of this by automatically locating a suitable driver when the DriverManager.getConnection() method is called. This feature is backward-compatible, so no changes are needed to the existing JDBC code.

8.What is JDBC Driver interface?

The JDBC Driver interface provides vendor-specific implementations of the abstract classes provided by the JDBC API. Each vendor driver must provide implementations of the java.sql.Connection,Statement,PreparedStatement, CallableStatement, ResultSet and Driver.

9.What does the connection object represents?

The connection object represents communication context, i.e., all communication with database is through connection object only.

10.What is Statement ?

Statement acts like a vehicle through which SQL commands can be sent. Through the connection object we create statement kind of objects.
Through the connection object we create statement kind of objects.

Statement stmt = conn.createStatement();

This method returns object which implements statement interface.

11.What is PreparedStatement?

A prepared statement is an SQL statement that is precompiled by the database. Through precompilation, prepared statements improve the performance of SQL commands that are executed multiple times (given that the database supports prepared statements). Once compiled, prepared statements can be customized prior to each execution by altering predefined SQL parameters.

PreparedStatement pstmt = conn.prepareStatement("UPDATE EMPLOYEES SET SALARY = ? WHERE ID = ?");

pstmt.setBigDecimal(1, 153833.00);

pstmt.setInt(2, 110592);

Here: conn is an instance of the Connection class and "?" represents parameters.These parameters must be specified before execution.

12.What is the difference between a Statement and a PreparedStatement?

Statement	PreparedStatement
A standard Statement is used to create a Java representation of a literal SQL statement and execute it on the database.	A PreparedStatement is a precompiled statement. This means that when the PreparedStatement is executed, the RDBMS can just run the PreparedStatement SQL statement without having to compile it first.
Statement has to verify its metadata against the database every time.	While a prepared statement has to verify its metadata against the database only once.
If you want to execute the SQL statement once go for STATEMENT	If you want to execute a single SQL statement multiple number of times, then go for PREPAREDSTATEMENT. PreparedStatement objects can be reused with passing different values to the queries

13.What are callable statements ?

Callable statements are used from JDBC application to invoke stored procedures and functions.

14.How to call a stored procedure from JDBC ?

PL/SQL stored procedures are called from within JDBC programs by means of the prepareCall() method of the Connection object created. A call to this method takes variable bind parameters as input parameters as well as output variables and creates an object instance of the CallableStatement class.

The following line of code illustrates this:

CallableStatement stproc_stmt = conn.prepareCall("{call procname(?,?,?)}");

Here conn is an instance of the Connection class.

15.What are types of JDBC drivers?

There are four types of drivers defined by JDBC as follows:

Type 1: JDBC/ODBC—These require an ODBC (Open Database Connectivity) driver for the database to be installed. This type of driver works by translating the submitted queries into equivalent ODBC queries and forwards them via native API calls directly to the ODBC driver. It provides no host redirection capability.
Type2: Native API (partly-Java driver)—This type of driver uses a vendor-specific driver or database API to interact with the database. An example of such an API is Oracle OCI (Oracle Call Interface). It also provides no host redirection.
Type 3: Open Protocol-Net—This is not vendor specific and works by forwarding database requests to a remote database source using a net server component. How the net server component accesses the database is transparent to the client. The client driver communicates with the net server using a database-independent protocol and the net server translates this protocol into database calls. This type of driver can access any database.
Type 4: Proprietary Protocol-Net(pure Java driver)—This has a same configuration as a type 3 driver but uses a wire protocol specific to a particular vendor and hence can access only that vendor's database. Again this is all transparent to the client.

Note: Type 4 JDBC driver is most preferred kind of approach in JDBC

16.Which type of JDBC driver is the fastest one?

JDBC Net pure Java driver(Type IV) is the fastest driver because it converts the JDBC calls into vendor specific protocol calls and it directly interacts with the database.

17.Does the JDBC-ODBC Bridge support multiple concurrent open statements per connection?

No. You can open only one Statement object per connection when you are using the JDBC-ODBC Bridge.

18.Which is the right type of driver to use and when?

Type I driver is handy for prototyping
Type III driver adds security, caching, and connection control
Type III and Type IV drivers need no pre-installation

19.What are the standard isolation levels defined by JDBC?

The values are defined in the class java.sql.Connection and are:

TRANSACTION_NONE
TRANSACTION_READ_COMMITTED
TRANSACTION_READ_UNCOMMITTED
TRANSACTION_REPEATABLE_READ
TRANSACTION_SERIALIZABLE

Any given database may not support all of these levels.

20.What is resultset ?

The ResultSet represents set of rows retrieved due to query execution.

ResultSet rs = stmt.executeQuery(sqlQuery);

21.What are the types of resultsets?

The values are defined in the class java.sql.Connection and are:

TYPE_FORWARD_ONLY specifies that a resultset is not scrollable, that is, rows within it can be advanced only in the forward direction.
TYPE_SCROLL_INSENSITIVE specifies that a resultset is scrollable in either direction but is insensitive to changes committed by other transactions or other statements in the same transaction.
TYPE_SCROLL_SENSITIVE specifies that a resultset is scrollable in either direction and is affected by changes committed by other transactions or statements within the same transaction.

Note: A TYPE_FORWARD_ONLY resultset is always insensitive.

22.What’s the difference between TYPE_SCROLL_INSENSITIVE and TYPE_SCROLL_SENSITIVE?

TYPE_SCROLL_INSENSITIVE	TYPE_SCROLL_SENSITIVE
An insensitive resultset is like the snapshot of the data in the database when query was executed.	A sensitive resultset does NOT represent a snapshot of data, rather it contains points to those rows which satisfy the query condition.
After we get the resultset the changes made to data are not visible through the resultset, and hence they are known as insensitive.	After we obtain the resultset if the data is modified then such modifications are visible through resultset.
Performance not effected with insensitive.	Since a trip is made for every ‘get’ operation, the performance drastically get affected.

22.What is rowset?

A RowSet is an object that encapsulates a set of rows from either Java Database Connectivity (JDBC) result sets or tabular data sources like a file or spreadsheet. RowSets support component-based development models like JavaBeans, with a standard set of properties and an event notification mechanism.

24.What are the different types of RowSet ?

There are two types of RowSet are there. They are:

Connected - A connected RowSet object connects to the database once and remains connected until the application terminates.
Disconnected - A disconnected RowSet object connects to the database, executes a query to retrieve the data from the database and then closes the connection. A program may change the data in a disconnected RowSet while it is disconnected. Modified data can be updated in the database after a disconnected RowSet reestablishes the connection with the database.

25.What is the need of BatchUpdates?

The BatchUpdates feature allows us to group SQL statements together and send to database server in one single trip.

26.What is a DataSource?

A DataSource object is the representation of a data source in the Java programming language. In basic terms,

A DataSource is a facility for storing data.

DataSource can be referenced by JNDI.

Data Source may point to RDBMS, file System , any DBMS etc..

27.What are the advantages of DataSource?

The few advantages of data source are :

An application does not need to hardcode driver information, as it does with the DriverManager.

The DataSource implementations can easily change the properties of data sources. For example: There is no need to modify the application code when making changes to the database details.
The DataSource facility allows developers to implement a DataSource class to take advantage of features like connection pooling and distributed transactions.

28.What is connection pooling? what is the main advantage of using connection pooling?

A connection pool is a mechanism to reuse connections created. Connection pooling can increase performance dramatically by reusing connections rather than creating a new physical connection each time a connection is requested..

Apache Axis Java Client

2011-06-30T09:56:00.000-07:00

package com;
import javax.xml.namespace.QName;
import javax.xml.rpc.ParameterMode;

import org.apache.axis.client.Call;
import org.apache.axis.client.Service;
import org.apache.axis.encoding.XMLType;

/**
*
* @author Vinaykumar.guntaka
* jaxrpc.jar
* commons-discover-0.2.jar
* wsdl4j-1.5.1.jar
* axis.jar
*/
public class Demo {
    public static String endpoint =   "http://localhost:8080/ProjectName/services/ProjectActions";
    public static void main(String[] args) {
        invokeMethod();
        invokeParamMethod();

    }

    public static void invokeMethod(){
        try {
            Service service = new Service();
            QName Qname = new QName(endpoint,"HelloWorld");
            Call call = (Call) service.createCall(Qname);
            call.setTargetEndpointAddress(new java.net.URL(endpoint));
              call.setProperty(Call.SOAPACTION_USE_PROPERTY, new Boolean(true));
                call.setProperty(Call.SOAPACTION_URI_PROPERTY,"http://localhost:8080/ProjectName/services/ProjectActions/HelloWorld");
                call.setOperationName(new QName("http://com","HelloWorld"));

                String ret = (String) call.invoke("HelloWorld", new Object[]{});

                System.out.println("Sent 'Hello!', got '" + ret + "'");
        } catch (Exception e) {
            // TODO: handle exception
        }
    }
    public static void invokeParamMethod(){
        try {
            Service service = new Service();
            QName Qname = new QName(endpoint,"getMessage");
            Call call = (Call) service.createCall(Qname);
            call.setTargetEndpointAddress(new java.net.URL(endpoint));
            call.setProperty(Call.SOAPACTION_USE_PROPERTY, new Boolean(true));
            call.setProperty(Call.SOAPACTION_URI_PROPERTY,"http://localhost:8080/ProjectName/services/ProjectActions/getMessage");
            call.setOperationName(new QName("http://com","getMessage"));

            call.addParameter("str", XMLType.XSD_STRING, ParameterMode.IN);
            call.addParameter("str1", XMLType.XSD_STRING, ParameterMode.IN);
            call.setReturnType(XMLType.XSD_STRING);
            String ret = (String) call.invoke( new Object[] { "Vinay!","Guntaka" } );

            System.out.println("got '" + ret + "'");
        } catch (Exception e) {
            // TODO: handle exception
        }

    }

    }

/*******************
Web service actions

*/

    public String getMessage(String str,String str1){
        return str+"Vinay Guntaka"+str1;

    }
    public String HelloWorld(){
        return "HelloWorld Vinay Guntaka";

    }

Spring Vs Struts

2011-05-25T10:23:00.000-07:00

Differences between Struts and Springs

Springs:

· Dependency Injection

· Inversion of Control

· Transaction Management

· Aspect Oriented Programming

· DB Connection Control

· Model View Controller (this is small part that is somehow comparable with Struts)

· Spring Web flow (define control flows).

· Spring is made up of many components, main component being the core container (Beans, BeanFactory, Application Context, etc) that provide the Dependency injection via a lightweight container, and the rest of the components (e.g. AOP, Transaction Management, etc.) are built around it.

Apache Struts is an open-source web application framework for developing Java EE web applications. It uses and extends the Java Servlet API to encourage developers to adopt a model-view-controller (MVC) architecture.

Spring is much more than Struts. Web MVC is just a small subset of the capabilities that Spring provides.

Struts is one of the first web MVC frameworks based on servlets and JSPs

Spring is a Java EE application framework based on Inversion of Control (IoC) and aspect-oriented programming (AOP).

Spring has a web MVC module that's analogous to Struts. Spring can also use Struts as its web MVC module.

Struts are basically a request based framework while spring is a component based framework. All the benefits of struts can be achieved through spring (Spring MVC). Spring has many modules which helps you develop enterprise application with different components like ORM, AOP, MVC, and Transaction management etc., With Spring 3.0 it has an inbuilt support for restful services too. Also spring portfolio has other project which seamlessly integrates with spring like spring security (Acegi security), osgi, spring web services and all. Over all spring offers more benefits than struts in developing a quality applications by enforcing good design and decoupled components

12 BENEFITS of Spring MVC over Struts

Spring is a powerful Java application framework, used in a wide range of Java applications. It provides enterprise services to Plain Old Java Objects (POJOs). Spring uses dependency injection to achieve simplification and increase testability.

1. Spring provides a very clean division between controllers, JavaBeans models, and views.

2. Spring’s MVC is very flexible. Unlike Struts, which forces your Action and Form objects into concrete inheritance (thus taking away your single shot at concrete inheritance in Java), Spring MVC is entirely based on interfaces. Furthermore, just about every part of the Spring MVC framework is configurable via plugging in your own interface. Of course we also provide convenience classes as an implementation option.

3. Spring, like WebWork, provides interceptors as well as controllers, making it easy to factor out behavior common to the handling of many requests.

4. Spring MVC is truly view-agnostic. You don’t get pushed to use JSP if you don’t want to; you can use Velocity, XLST or other view technologies. If you want to use a custom view mechanism

– for example, your own templating language – you can easily implement the Spring View interface to integrate it.

5. Spring Controllers are configured via IoC like any other objects. This makes them easy to test, and beautifully integrated with other objects managed by Spring.

6. Spring MVC web tiers are typically easier to test than Struts web tiers, due to the avoidance of forced concrete inheritance and explicit dependence of controllers on the dispatcher servlet.

7. The web tier becomes a thin layer on top of a business object layer. This encourages good practice. Struts and other dedicated web frameworks leave you on your own in implementing your business objects; Spring provides an integrated framework for all tiers of your application.

8. No ActionForms. Bind directly to domain objects

9. More testable code (validation has no dependency on Servlet API)

10. Struts imposes dependencies on your Controllers (they must extend a Struts class), Spring doesn’t force you to do this although there are convenience Controller implementations that you can choose to extend.

11. Spring has a well defined interface to business layer

12. Spring offers better integration with view technologies other than JSP (Velocity / XSLT / Free Marker / XL etc.)

Collection FrameWork in Java

2011-05-10T17:38:00.000-07:00

Concrete Collections
--------------------

Concrete Collection Implements description

HashSet Set Hashtable
TreeSet SortedSet Balance binary Tree
ArrayList List Re-sizable array
LinkedList List LinkedList
Vector List re-sizable array
HashMap Map hashtable
TreeMap SortedMap balance binary tree
HashTable Map hashtable

/**
*
*/
package com.jit;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.Vector;

/**
* @author Vinay Guntaka
* Factors of Collection Framework to be considered
* API
* Synchronization
* Data growth
* Usage patterns
*/
public class CollectionFrameWork {

public static void main(String[] args) {
getHashSet();
getTreeSet();
getArrayList();
getLinkedList();
getVectorList();
getHashMap();
getHashTable();
getTreeMap();

}

/*
* Unordered (A HashSet use the hash function to store the values)
* No Duplicates
* Allow Null
*/

public static void getHashSet()
{
Set<String> hs = new HashSet<String>();
hs.add("Vinay");
hs.add("Vinay");
hs.add("Kumar");
hs.add("Guntaka");
hs.add(null);
System.out.println(hs);
}
/* A TreeSet is more efficient in case of search element.
* null throws NullPointerException
* By Default Sorted
* No Duplicates
*/
public static void getTreeSet()
{
Set<String> ts = new TreeSet<String>();
ts.add("Vinay");
ts.add("Vinay");
ts.add("Kumar");
ts.add("Guntaka");
ts.add("");
System.out.println(ts);

}

/**
* If you need to support random access, without inserting or removing
* elements from any place other than the end, then ArrayList offers the optimal collection.
* If, however, you need to frequently add and remove elements from the middle of the list and
* only access the list elements sequentially, then LinkedList offers the better implementation.
*
*/

/*
* Ordered
* Allows Null
* Allows Duplicates
* Iterating from To-And-Fro Directions
* Not Synchronized
*/

public static void getArrayList(){
List<String> al= new ArrayList<String>();
al.add("Vinay");
al.add(null);
al.add("Vinay");
al.add("Guntaka");
System.out.println(al);
// Iterating from Back Side
ListIterator<String> lsitr = al.listIterator(al.size());
while(lsitr.hasPrevious()){
System.out.println(lsitr.previous());
}
// Iterating from front Side
while(lsitr.hasNext()){
System.out.println(lsitr.next());
}
al.subList(0, 2).clear();
System.out.println(al);
}
/**
* In a LinkedList, each element is linked to its previous and next element making
* it easier to delete or insert in the middle of the list
*/

public static void getLinkedList(){
List<String> ll= new LinkedList<String>();
ll.add("Vinay");
ll.add(null);
ll.add("Vinay");
ll.add("Guntaka");
System.out.println(ll);

}

/*
* Synchronized
*/
public static void getVectorList(){
Vector<String> v = new Vector<String>();
v.add("Vinay");
v.add("Kumar");
v.add(null);
v.add("Guntaka");
v.add("Guntaka");
System.out.println(v);

}
/*
* Key Name should be Unique
* Unidentified Order
* UnSynchronized
* The values can be null.
*/

public static void getHashMap(){
Map<String,String> hm = new HashMap<String, String>();
hm.put("FName", "Vinay");
hm.put("MName", "Kumar");
hm.put("LName", "Guntaka");
hm.put("MName", null);
System.out.println(hm);
}
/*
* Key Name should be Unique
* Does not let you have null value for key.
* Synchronized
*/
public static void getHashTable(){
Map<String,Integer> ht = new Hashtable<String, Integer>();
ht.put("FName", 100);
ht.put("MName", 99);
ht.put("LName", 101);
ht.put("Name", 152);
System.out.println(ht);
}
/*
* The values can be null. But the key should be unique
* UnSynchronized
*/
public static void getTreeMap(){
Map<String,Integer> tm = new TreeMap<String, Integer>();
tm.put("FName", 100);
tm.put("MName", 99);
tm.put("LName", 101);
tm.put("Name", null);
System.out.println(tm);
}

}

Google Maps on Android Mobile / Simulator

2011-05-07T19:00:00.000-07:00

Loading the Google Maps on Android Mobile / Simulator

Follow the following link to generate the map key

http://code.google.com/android/add-ons/google-apis/mapkey.html

Command to load the debug.keystore

C:\Java\jre\bin>keytool.exe -list -alias androiddebugkey -keystore "C:\Documents and Settings\jit\.android\debug.keystore" -storepass android -keypass android

on Enter you will get a privateKeyEntry with Certficate FingerPrint (MD5)

Once the MD5 finger print is generated

Registering the Certificate Fingerprint with the Google Maps Service
http://code.google.com/android/maps-api-signup.html

Note: Make sure the simluator is set to Google 2.X API

Program to Load Google MAP on Android

--------------------------------------
main.xml
--------------------------------------

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<com.google.android.maps.MapView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/webview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:clickable="true"
android:enabled="true"
android:apiKey="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
/>
</LinearLayout>

----------------------------------------
AndroidManifest.xml
----------------------------------------
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.jit"
android:versionCode="1"
android:versionName="1.0">

<application android:icon="@drawable/icon" android:label="@string/app_name">
<uses-library android:name="com.google.android.maps" />
<activity android:name=".GMap"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

<uses-permission android:name="android.permission.ACCESS_LOCATION_EXTRA_COMMANDS"></uses-permission>

</manifest>

------------------------------------------------
GMAP.Java
-------------------------------------------------

package com.jit;
/*
* @author: Vinay Guntaka
*/
import android.os.Bundle;
import android.view.MotionEvent;
import android.widget.Toast;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapController;
import com.google.android.maps.MapView;

public class GMap extends com.google.android.maps.MapActivity{
MapController mMapController;
MapView mMapView;
GeoPoint p;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mMapView = (MapView) findViewById(R.id.webview);
mMapView.setBuiltInZoomControls(true);

mMapView.setSatellite(true);

mMapController = mMapView.getController();
mMapController.setZoom(15);
//mMapView.setSatellite(true);
mMapView.setStreetView(true);
String coordinates[] = {"1.352566007", "103.78921587"};
double lat = Double.parseDouble(coordinates[0]);
double lng = Double.parseDouble(coordinates[1]);

p = new GeoPoint(
(int) (lat * 1E6),
(int) (lng * 1E6));

mMapController.animateTo(p);
mMapController.setZoom(17);
mMapView.invalidate();

/* MyOverlays myOverlays = new MyOverlays(this.getResources().getDrawable(R.drawable.icon), this);

OverlayItem tempOverlayItem = new OverlayItem(new GeoPoint(17000000,78000000), "NewActivity", "Welcome to New Activity");
tempOverlayItem.setMarker(this.getResources().getDrawable(R.drawable.icon));

myOverlays.addOverlay(tempOverlayItem);

mMapView.getOverlays().add(myOverlays);*/

}
@Override
public boolean onTouchEvent(MotionEvent event) {
Toast.makeText(this, "Ooops! I am touched", Toast.LENGTH_LONG).show();
return super.onTouchEvent(event);
}

@Override
protected boolean isRouteDisplayed() {
// TODO Auto-generated method stub
return false;
}

}

------------------------------------------

Ajax Programming setup instructions

2011-05-07T18:35:00.000-07:00

Ajax Programming :

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
</HEAD>
<script type="text/javascript" language="javascript">
// function to create an XMLHttpClient in a cross-browser manner
function getAJAXRequest() {
var xmlhttp=null;;
try {
// Mozilla / Safari / IE7
xmlhttp = new XMLHttpRequest();
} catch (e) {
// IE
var XMLHTTP_IDS = new Array('MSXML2.XMLHTTP.5.0',
'MSXML2.XMLHTTP.4.0',
'MSXML2.XMLHTTP.3.0',
'MSXML2.XMLHTTP',
'Microsoft.XMLHTTP' );
var success = false;
for (var i=0;i < XMLHTTP_IDS.length && !success; i++) {
try {
xmlhttp = new ActiveXObject(XMLHTTP_IDS[i]);
success = true;
break;
} catch (e) {}
}
if (!success) {
return null;
}
}
return xmlhttp;
}

function loadAjaxCall(){

var http_request=getAJAXRequest();
//open(method,url,async)
//Specifies the type of request, the URL, and if the request should be handled asynchronously or not.
//method: the type of request: GET or POST
//url: the location of the file on the server
//async: true (asynchronous) or false (synchronous)

var parameters="one="+FristVal+"&sec="+SecVal;

//Note: When you use async=false, do NOT write an onreadystatechange function - just put the code after the send() statement:
//Note: When using async=true, specify a function to execute when the response is ready in the onreadystatechange event:

http_request.open('POST', "/projectName/SomeAction.do", false);
http_request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
http_request.setRequestHeader("Content-length", parameters.length);
http_request.setRequestHeader("Connection", "close");
http_request.send(parameters);

// here the state is synch
// getting the response as responseText or responseXML
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;

/*
* Suppose if Asynch we are have to set the readyState
// here the response is in ready state
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
}
*
*/
// onreadystatechange Stores a function (or the name of a function) to be called automatically each time the readyState property changes
//readyState :-
//Holds the status of the XMLHttpRequest. Changes from 0 to 4:

//0: request not initialized
//1: server connection established
//2: request received
//3: processing request
//4: request finished and response is ready

//status:-
//200: "OK"
//404: Page not found

}

</script>

<BODY>

</BODY>
</HTML>

Captcha Programming

2011-05-07T18:31:00.000-07:00

Captcha Programming in Java

package com.jit;

import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Iterator;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* @author Vinay Guntaka
* Servlet implementation class CaptchaServlet
*/
public class CaptchaServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#HttpServlet()
*/
public CaptchaServlet() {
super();
}

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
createCatcha(request, response);
}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
createCatcha(request, response);
}
@SuppressWarnings("unchecked")
protected void createCatcha(HttpServletRequest request,HttpServletResponse response)throws ServletException, IOException {

response.setContentType("image/jpg");

try {
Color textColor = Color.white;
Font textFont = new Font("Georgia", Font.PLAIN, 18);
int charsToPrint = 6;
int width = 125;
int height = 28;
float horizMargin = 20.0f;
float imageQuality = 0.95f; // max is 1.0 (this is for jpeg)
double rotationRange = 0.7; // this is radians
BufferedImage bufferedImage = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);

Graphics2D g = (Graphics2D) bufferedImage.getGraphics();

// Draw an oval
g.setColor(new Color(255, 153, 0));
g.fillRect(0, 0, width, height);
g.setColor(textColor);
g.setFont(textFont);

FontMetrics fontMetrics = g.getFontMetrics();
int maxAdvance = fontMetrics.getMaxAdvance();
int fontHeight = fontMetrics.getHeight();

// i removed 1 and l and i because there are confusing to users...
// Z, z, and N also get confusing when rotated
// 0, O, and o are also confusing...
// lowercase G looks a lot like a 9 so i killed it
// this should ideally be done for every language...
// i like controlling the characters though because it helps prevent
// confusion
String elegibleChars = "ABCDEFGHJKLMPQRSTUVWXYabcdefhjkmnpqrstuvwxy23456789";
char[] chars = elegibleChars.toCharArray();

float spaceForLetters = -horizMargin * 2 + width;
float spacePerChar = spaceForLetters / (charsToPrint - 1.0f);
StringBuffer finalString = new StringBuffer();

for (int i = 0; i < charsToPrint; i++) {
double randomValue = Math.random();
int randomIndex = (int) Math.round(randomValue*(chars.length - 1));
char characterToShow = chars[randomIndex];
finalString.append(characterToShow);
int charWidth = fontMetrics.charWidth(characterToShow);
int charDim = Math.max(maxAdvance, fontHeight);
int halfCharDim = (int) (charDim / 2);

BufferedImage charImage = new BufferedImage(charDim, charDim,BufferedImage.TYPE_INT_ARGB);
Graphics2D charGraphics = charImage.createGraphics();
charGraphics.translate(halfCharDim, halfCharDim);
double angle = (Math.random() - 0.5) * rotationRange;
charGraphics.transform(AffineTransform.getRotateInstance(angle));
charGraphics.translate(-halfCharDim, -halfCharDim);
charGraphics.setColor(textColor);
charGraphics.setFont(textFont);

int charX = (int) (0.5 * charDim - 0.5 * charWidth);
charGraphics.drawString("" + characterToShow,charX,
(int) ((charDim - fontMetrics.getAscent()) / 2 + fontMetrics
.getAscent()));

float x = horizMargin + spacePerChar * (i) - charDim / 2.0f;
int y = (int) ((height - charDim) / 2);
g.drawImage(charImage, (int) x, y, charDim, charDim,null, null);

charGraphics.dispose();
}

// Write the image as a jpg
Iterator iter = ImageIO.getImageWritersByFormatName("JPG");
if (iter.hasNext()) {
ImageWriter writer = (ImageWriter) iter.next();
ImageWriteParam iwp = writer.getDefaultWriteParam();
iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
iwp.setCompressionQuality(imageQuality);
writer.setOutput(ImageIO.createImageOutputStream(response.getOutputStream()));
IIOImage imageIO = new IIOImage(bufferedImage, null, null);
writer.write(null, imageIO, iwp);
} else {
throw new RuntimeException("no encoder found for jsp");
}

// let's stick the final string in the session
request.getSession().setAttribute("captcha", finalString.toString());
g.dispose();

} catch (IOException ioe) {
throw new RuntimeException("Unable to build image", ioe);
}

}

}

----------------------------------
Captcha.jsp

<%@page contentType="text/html" pageEncoding="UTF-8"%>

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Captcha</title>
<link rel="stylesheet" href="style.css">
</head>
<body>
<center>
<form method="post">
<table cellspacing="15">
<tr>
<td>Are you human?</td>
<td><input type="text" name="code"></td>
</tr>

</table>

<br>
<img src="CaptchaServlet">

<br><br>
<input type="submit" value="submit">

</form>
<br><br>
<%
String captcha = (String) session.getAttribute("captcha");
String code = (String) request.getParameter("code");

if (captcha != null && code != null) {

System.out.println("Captcha Code:"+captcha);
System.out.println("Code:"+code);

if (captcha.equals(code)) {
out.print("<p class='alert'>Correct</p>");
} else {
out.print("<p class='alert'>Incorrect</p>");
}
}
%>
</center>
</body>
</html>

--------------------------------
web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<display-name>Captcha</display-name>
<welcome-file-list>
<welcome-file>captcha.jsp</welcome-file>
</welcome-file-list>
<servlet>
<description></description>
<display-name>CaptchaServlet</display-name>
<servlet-name>CaptchaServlet</servlet-name>
<servlet-class>com.jit.CaptchaServlet</servlet-class>;
</servlet>
<servlet-mapping>
<servlet-name>CaptchaServlet</servlet-name>
<url-pattern>/CaptchaServlet</url-pattern>
</servlet-mapping>
</web-app>

Configure JNDI Connection Pooling:

2011-04-23T21:25:00.000-07:00

Configure JNDI Connection Pooling:

For establishing the connection pool i have created a dynamic web-project with SampleConn, with MySql Database and loggers. So, make sure we have the mysql.jar in tomcat working lib directory and log4j.jar in your project library.

Here i am listing out the steps to follow:

------------------------------------------------------------------------------------------
Step 1) Configure web.xml file

Here i am invoking a servlet on startup of server (GetConnPool)

---------------------------------------------------
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<display-name>SampleConn</display-name>
<resource-ref>
    <description>DB Connection</description>
    <res-ref-name>jdbc/JIT</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
</resource-ref>
<servlet>
    <servlet-name>Connection</servlet-name>
    <servlet-class>com.jit.servlets.GetConnPool</servlet-class>;
    <load-on-startup>1</load-on-startup>
</servlet>
<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
----------------------------------------------------------------

Step 2) Create a context.xml in META-INF of your Project

-----------------------------------------------------------------

<?xml version="1.0" encoding="UTF-8"?>

<Context privileged="true" antiResourceLocking="false"
    antiJARLocking="false" debug="1" reloadable="true" path="">

    

    

    

    

    

    


    <Resource name="jdbc/JIT" auth="Container" type="javax.sql.DataSource"
         username="root"
         password="root" maxActive="-1" maxIdle="-1" maxWait="-1"
         driverClassName="com.mysql.jdbc.Driver"
         url="jdbc:mysql://localhost:3306/sample?autoReconnect=true"
         />

</Context>

--------------------------------------------------------------------

Step 3) Configure your log4j.properties file in your project source directory

--------------------------------------------------------------------

# Set root category priority to INFO and its only appender to CONSOLE.
log4j.rootCategory=DEBUG, CONSOLE
#log4j.rootCategory=INFO, CONSOLE, LOGFILE

# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE

# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=DEBUG
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=[%d{dd MMM yyyy HH:mm:ss}] %l - %m%n

# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.Threshold=DEBUG
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=[%d{dd MMM yyyy HH:mm:ss}] %l - %m%n

log4j.logger.org.apache.commons.digester.Digester=info

--------------------------------------------------------------------
Step 4) GetConnPool.java
Here in the init() i am invoking & closing the connection

---------------------------------------------------------------------
package com.jit.servlets;
/**
* @author Vinay Guntaka
*/
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.jit.connections.ConnectionUtil;

/**
* Servlet implementation class GetConnPool
*/
public class GetConnPool extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public GetConnPool() {
        super();
        // TODO Auto-generated constructor stub
    }
     @Override
    public void init() throws ServletException {
        // TODO Auto-generated method stub
        super.init();

        ConnectionUtil.closeConnection(ConnectionUtil.getConnection());
    }

    /**
    * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

    /**
    * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

------------------------------------------------
Step 5) ConnectionUtil.Java

This is the main program that we are fetching the JNDI Connection Pool Object
------------------------------------------------
package com.jit.connections;
/**
* @author Vinay Guntaka
*/
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.sql.DataSource;

import org.apache.log4j.Logger;

public class ConnectionUtil
{
    //Initlizing the Logger
    private static final Logger logger = Logger.getLogger(ConnectionUtil.class);

    public static Connection getConnection() {
        Connection conn = null;
        try {
            Context initCtx = new InitialContext();
            Context envCtx = (Context) initCtx.lookup("java:comp/env");
            DataSource ds = (DataSource) envCtx.lookup("jdbc/JIT");
            conn = ds.getConnection();
            if (conn != null) {
                logger.info("Successfully Obtained Connection From ConnectionPool");
            }
            return conn;
        } catch (SQLException se) {
            logger.error(se.getMessage());
        } catch (Exception e) {
            logger.error(e.getMessage());
        }
        return conn;
    }
    public static Connection closeConnection(Connection conn){
        try {
            if(conn != null){
                conn.close();
                conn = null;
                logger.info("Successfully Closed Connection From ConnectionPool");

            }
        } catch (SQLException se) {
            logger.error(se.getMessage());
        } catch (Exception e) {
            logger.error(e.getMessage());
        }
        return conn;
    }


}
----------------------------------------------------------------------

Retrieving multiple result sets from a stored procedure in a JDBC application

2011-04-18T17:25:00.000-07:00

Hello,

Retrieving multiple result sets and OUT Parameters by passing IN Parameter from a stored procedure in a JDBC application.

Connection File:

package com.jit;

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
/**
* @author Vinay Guntaka
* Retrieving multiple result sets from a stored procedure in a JDBC application
* All Connections are Configured in this Class
*/
public class ConnectionUtil {


    public static Connection closeConnection(Connection conn){
        try {
            if(conn != null){
                conn.close();
                conn = null;
            }
        } catch (SQLException se) {
            System.out.println(se.getMessage());
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
        return conn;
    }

    public static CallableStatement closeCallableStatement(CallableStatement clst){
        try{
            if(clst !=null){
                clst.close();
                clst = null;
            }
            }catch (SQLException e) {
                System.err.println(e.getMessage());
            }
            return clst;
        }



    public static ResultSet closeResultSet(ResultSet resultSet){
        try {
            if(resultSet != null){
                resultSet.close();
                resultSet = null;
            }
        } catch (SQLException se) {
            System.out.println(se.getMessage());
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }

        return resultSet;
    }



    public static Connection getLocalConnection() {
        Connection conn = null;
        try {

            Class.forName("com.mysql.jdbc.Driver").newInstance();
            String url = "jdbc:mysql://localhost:3306/sample";
            conn = DriverManager.getConnection(url, "root", "root");

            if (conn != null) {
                System.out.println("Successfully Obtained Connection From ConnectionPool");
            }
            return conn;
        } catch (SQLException se) {
            System.out.println(se.getMessage());
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
        return conn;
    }
}

Main Program To Execute Procedure:

package com.jit;

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Types;
/**
* @author Vinay Guntaka
* We are Fetching the Results from MySQL Procedure by passing
* one IN Param and fetching One OUT Param with Multiple Result sets.
*/
public class CallProcedure {
    public static void main(String[] args) {
        Connection conn =null;
        CallableStatement callStmt = null;
        ResultSet rs =null;

        try {
            conn = ConnectionUtil.getLocalConnection();
            callStmt = conn.prepareCall("call proc_getData(?,?)");
            //Passing param to Execute First Query
            callStmt.setInt(1, 22);
            //Registering the Out Parameter
            callStmt.registerOutParameter(2,Types.VARCHAR);
            //Fetching the First RS of OUT Param
            callStmt.execute();
            String outParam = callStmt.getString(2);           ; // OUT parameter
            System.out.println("First Result Set Out Param:-"+outParam);
            //Fetching the Second Result Set from Procedure
            rs = callStmt.executeQuery();
            while(rs.next()){
                System.out.println("Second Query Result Set");
                System.out.println(rs.getString(1));
                System.out.println(rs.getString(2));
                System.out.println(rs.getString(3));
                System.out.println(rs.getString(4));
                System.out.println(rs.getString(5));
            }
            //Checking is there any more result sets
            if(callStmt.getMoreResults())
            {
                System.out.println("One More Result Set is there");
                //Fetching the Thrid Result Set from the Procedure
                rs = callStmt.executeQuery();
                while(rs.next()){
                    System.out.println("Thrid Query Result Set");
                    System.out.println(rs.getString(1));
                    System.out.println(rs.getString(2));
                    System.out.println(rs.getString(3));
                    System.out.println(rs.getString(4));
                    System.out.println(rs.getString(5));
                }
            }else
            {
                System.out.println("No More Results Sets");
            }
        } catch (Exception e) {
            System.err.println(e.getMessage());
        }finally
        {
            //Closing all connections
            ConnectionUtil.closeConnection(conn);
            ConnectionUtil.closeCallableStatement(callStmt);
            ConnectionUtil.closeResultSet(rs);
        }

    }
}

Here is the procedure:

DELIMITER $$

DROP PROCEDURE IF EXISTS `sample`.`proc_getData`$$

CREATE DEFINER=`root`@`localhost` PROCEDURE `proc_getData`(in user_id int,out user_name varchar(64))
BEGIN
    select user_name from users where id=user_id into user_name ;
    select * from employee;
    select * from users;

    END$$

DELIMITER ;

Installing an SSL Certificate in Tomcat 4.x/5.x/6.x

2011-03-31T17:56:00.000-07:00

Installing an SSL Certificate in Tomcat 4.x/5.x/6.x

http://help.securepaynet.net/article/5239

SHA Alogorithm in Java

2011-03-31T17:53:00.001-07:00

import java.security.MessageDigest;

public class Util {
    public static String getSHA(String text)throws Exception{
        MessageDigest md;
        md = MessageDigest.getInstance("SHA-1");
        md.update(text.getBytes("iso-8859-1"), 0, text.length());
        return convertToHex(md.digest());
    }
    private static String convertToHex(byte[] data) {
            StringBuffer buf = new StringBuffer();
            for (int i = 0; i < data.length; i++) {
                int halfbyte = (data[i] >>> 4) & 0x0F;
                int two_halfs = 0;
                do {
                    if ((0 <= halfbyte) && (halfbyte <= 9))
                        buf.append((char) ('0' + halfbyte));
                    else
                        buf.append((char) ('a' + (halfbyte - 10)));
                    halfbyte = data[i] & 0x0F;
                } while(two_halfs++ < 1);
            }
            return buf.toString();
    }

    public static void main(String[] args) throws Exception {
        System.out.println(Util.getSHA("Vinay Guntaka"));

    }

}

Generating Unique Number in Java

2011-03-31T17:51:00.000-07:00

import java.util.Random;

public class UniqueIDGenerator {

    private static final long serialVersionUID = 1L;

    /**
    *
    * Random-number generator.
    */

    private static transient Random r = new Random();

    // use constanst to prevent warnings about magic numbers:

    private static final long HEX_3FFFFFFFFFFFFFFF = 0x3FFFFFFFFFFFFFFFL;

    private static final long HEX_8000000000000000 = 0x8000000000000000L;

    private static final long HEX_FFFFFFFFFFFF0FFF = 0xFFFFFFFFFFFF0FFFL;

    private static final long HEX_4000 = 0x4000;

    private static final long HEX_FFFFFFFF00000000 = 0xFFFFFFFF00000000L;

    private static final long HEX_FFFFFFFF = 0xFFFFFFFFL;

    private static final long HEX_FFFF0000 = 0xFFFF0000L;

    private static final long HEX_0000000000000000FFFF = 0x0000000000000000FFFFL;

    private static final long HEX_FFFF000000000000 = 0xFFFF000000000000L;

    private static final long HEX_FFFF = 0xFFFF;

    private static final long HEX_FFFFFFFFFFFF = 0xFFFFFFFFFFFFL;

    private static final int DEC_4 = 4;

    private static final int DEC_8 = 8;

    private static final int DEC_12 = 12;

    private static final int DEC_16 = 16;

    private static final int DEC_32 = 32;

    private static final int DEC_48 = 48;

    /**
    *
    * @return a string with a universally unique id of format:
    *
    *         xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx .
    */

    public static String generateUUID() {

        // calculate lsb and msb

        long leastSigBits = r.nextLong();

        long mostSigBits = r.nextLong();

        leastSigBits &= HEX_3FFFFFFFFFFFFFFF;

        leastSigBits |= HEX_8000000000000000; // set top two bits to variant 2

        mostSigBits &= HEX_FFFFFFFFFFFF0FFF;

        mostSigBits |= HEX_4000; // Version 4;

        // turn leastSigBits and mostSigBits into string of format:

        // xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

        String id =

        padHex(((mostSigBits & HEX_FFFFFFFF00000000) >> DEC_32) & HEX_FFFFFFFF,
                DEC_8)

                + "-"

                + padHex(((mostSigBits & HEX_FFFF0000) >> DEC_16), DEC_4)

                + "-"

                + padHex((mostSigBits & HEX_0000000000000000FFFF), DEC_4)

                + "-"

                + padHex(
                        (((leastSigBits & HEX_FFFF000000000000) >> DEC_48) & HEX_FFFF),
                        DEC_4)

                + "-"

                + padHex(leastSigBits & HEX_FFFFFFFFFFFF, DEC_12);

        return id;

    }

    /**
    *
    * Returns a hex String from l, padded to n spaces.
    *
    * @param l
    *            .
    *
    * @param n
    *            .
    *
    * @return String
    */

    private static String padHex(long l, int n) {

        String s = Long.toHexString(l);

        while (s.length() < n) {

            s = "0" + s;

        }

        return s;

    }
    public static void main(String[] args) {
        System.out.println(generateUUID());
    }

}

Improving the Performance of a JDBC Program

2010-11-28T04:44:00.000-08:00

A java program that uses JDBC to connect to a database and retrieve the data from the database may take some time to perform these tasks. To know how much time has been taken by a JDBC program. we can take the help of currentTimeMillis() method of System class. This method gives the current time in milliseconds since January 1st 1970.

By Reducing the execution time of a JDBC Program, we can improve its performance. The execution time of a JDBC program depends on the Following factors:

The driver used to connect to the database will influence the execution time. Each driver will exhibit different performance and hence, selecting a good driver that gives optimum performance will improve the performance of a JDBC program.
setFetchSize() method of statement interface is useful to tell the driver how many rows at a time to be fetched from the database. By increasing the number of rows to be retrieved at a time, it is possible to improve the performance of a JDBC program.
Sometimes PreparedStatment inteface can be used in place of Statement interface for improving the performance.

Affect of PerparedStatement:

Using the PreparedStatement in place of Statement Interface will improve the performance of a JDBC program.

When a SQL Statement is sent to database, the following tasks are performed:

The SQL Statement's Syntax should be verified to know whether it is correct or not. The SQL statement is divided into small pieces called "tokens". These tokens are also verified to know whether they are in SQL format or not.
Then another verification is done to know whether the table or view mentioned in the statement exists or not.

The above two statements are called "parsing" and takes some time. When the SQL Statement is executed, Statement interface does parsing every time the statement is executed.

On the Other hand if we use preparedStatement, it does parsing only once.
This saves time and hence PreparedStatement offers better Performance.

Thanks
Vinay Guntaka

Java Database Conntectivity

2010-11-28T04:24:00.000-08:00

Stages in JDBC Porgram:

Registering the Driver
Connecting to the Database
Preparing SQL Statements in java
Executing the SQL Statements on the Database
Retrieving the Results.
Closing the Connections.

A List of JDBC Drivers:

If you need to access a database with Java, you need a driver. This is a list of the drivers available, what database they can access, who makes it, and how to contact them.

IBM DB2
        jdbc:db2://<HOST>:<PORT>/<DB>
        com.ibm.db2.jdbc.app.DB2Driver

JDBC-ODBC Bridge
        jdbc:odbc:<DB>
        sun.jdbc.odbc.JdbcOdbcDriver
Microsoft SQL Server
        jdbc:weblogic:mssqlserver4:<DB>@<HOST>:<PORT>
        weblogic.jdbc.mssqlserver4.Driver
Oracle Thin
        jdbc:oracle:thin:@<HOST>:<PORT>:<SID>
        oracle.jdbc.driver.OracleDriver
PointBase Embedded Server
        jdbc:pointbase://embedded[:<PORT>]/<DB>
        com.pointbase.jdbc.jdbcUniversalDriver
Cloudscape
        jdbc:cloudscape:<DB>
        COM.cloudscape.core.JDBCDriver
Cloudscape RMI
        jdbc:rmi://<HOST>:<PORT>/jdbc:cloudscape:<DB>
        RmiJdbc.RJDriver
Firebird (JCA/JDBC Driver)
        jdbc:firebirdsql:[//<HOST>[:<PORT>]/]<DB>
        org.firebirdsql.jdbc.FBDriver
IDS Server
        jdbc:ids://<HOST>:<PORT>/conn?dsn='<ODBC_DSN_NAME>'
        ids.sql.IDSDriver
Informix Dynamic Server
        jdbc:informix-sqli://<HOST>:<PORT>/<DB>:INFORMIXSERVER=<SERVER_NAME>
        com.informix.jdbc.IfxDriver
InstantDB (v3.13 and earlier)
        jdbc:idb:<DB>
        jdbc.idbDriver
InstantDB (v3.14 and later)
        jdbc:idb:<DB>
        org.enhydra.instantdb.jdbc.idbDriver
Interbase (InterClient Driver)
        jdbc:interbase://<HOST>/<DB>
        interbase.interclient.Driver
Hypersonic SQL (v1.2 and earlier)
        jdbc:HypersonicSQL:<DB>
        hSql.hDriver
Hypersonic SQL (v1.3 and later)
        jdbc:HypersonicSQL:<DB>
        org.hsql.jdbcDriver
Microsoft SQL Server (JTurbo Driver)
        jdbc:JTurbo://<HOST>:<PORT>/<DB>
        com.ashna.jturbo.driver.Driver
Microsoft SQL Server (Sprinta Driver)
        jdbc:inetdae:<HOST>:<PORT>?database=<DB>
        com.inet.tds.TdsDriver
Microsoft SQL Server 2000 (Microsoft Driver)
        jdbc:microsoft:sqlserver://<HOST>:<PORT>[;DatabaseName=<DB>]
        com.microsoft.sqlserver.jdbc.SQLServerDriver
MySQL (MM.MySQL Driver)
        jdbc:mysql://<HOST>:<PORT>/<DB>
        com.mysql.jdbc.Driver
Oracle OCI 8i
        jdbc:oracle:oci8:@<SID>
        oracle.jdbc.driver.OracleDriver
Oracle OCI 9i
        jdbc:oracle:oci:@<SID>
        oracle.jdbc.driver.OracleDriver
PostgreSQL (v6.5 and earlier)
        jdbc:postgresql://<HOST>:<PORT>/<DB>
        postgresql.Driver
PostgreSQL (v7.0 and later)
        jdbc:postgresql://<HOST>:<PORT>/<DB>
        org.postgresql.Driver
Sybase (jConnect 4.2 and earlier)
        jdbc:sybase:Tds:<HOST>:<PORT>
        com.sybase.jdbc.SybDriver
Sybase (jConnect 5.2)
        jdbc:sybase:Tds:<HOST>:<PORT>
        com.sybase.jdbc2.jdbc.SybDriver

----------------------------------------------

Here i am writing a sample code for JDBC.

try

{
  Class.forName("Driver name");

  // DriverManager.registerDriver(new Drivername()); 
   Connection con = DriverManager.getConnenction("jdbcurl","username","password");
   Statement st = con.createStatement();

  ResultSet rs= st.executeQuery("select * from Tablename");

  While(){}

  rs.close();

  st.close();

  conn.close(); 
}
catch(Exception e)
{
}

Thanks

Vinay Guntaka

A Brief History of Java and JDBC

2010-11-27T21:43:00.000-08:00

Drools 5.0 plugin Installation to Eclipse3.5 Galileo

2010-11-17T09:52:00.000-08:00

Drools 5.0 Installation:

------------------------
Drools is a business rule management system (BRMS) with a forward chaining inference based rules engine, more correctly known as a production rule system, using an enhanced implementation of the Rete algorithm.

Drools 5.0 plugin Installation to Eclipse3.5 Galileo

Step 1:

Pls download the eclipse 3.5 Galileo (190mb) from the following link

http://www.eclipse.org/downloads/download.php?file=/technology/epp/downloads/release/galileo/SR2/eclipse-jee-galileo-SR2-win32.zip

Step 2:

Download the Drools 5.0 workbench from the following link:

http://download.jboss.org/drools/release/5.0.1.26597.FINAL/drools-5.0-eclipse-all.zip

Step 3:

Extract both files to Eclipse-jee-galileo-SR2-win32 and drools-5.0-eclipse-all

copy the FEATURES and PLUG-INS of Drools 5.0 and paste it in the respective Eclipse-jee-galileo-SR2-win32

Step 4:

Just Restart the Eclipse and go to Windows->Prefrences->Drools->Installed Drools Runtime
give the path of the extracted files of the Drools Dir
set ok and plz once again restart the eclipse so that the Drools Perspective will be installed to that
eclipse

Step 5:

Simply You can select the New Project Drools and execute the Drools
and have a great exp with Drools

Thanks
GVK

Generic XML Parsing Method

2010-11-17T09:46:00.000-08:00

Vinay Guntaka

Java Programmer

import java.io.StringReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;

public class ParseXML {
public Map<List<String>,Integer> parseXMLData(String xmlData,String rootTag,List<String> childTags)
{
Map<List<String>, Integer > xmlMap = new HashMap<List<String>,Integer>();

try {

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = dbf.newDocumentBuilder();
Document document = builder.parse(new InputSource(new StringReader(xmlData)));
NodeList nodeLst = document.getElementsByTagName(rootTag);
for (int s = 0; s < nodeLst.getLength(); s++) {
List<String> subItems = new ArrayList<String>();
for (int count = 0; count < childTags.size(); count++) {
Node fstNode = nodeLst.item(s);
if (fstNode.getNodeType() == Node.ELEMENT_NODE) {
Element fstElmnt = (Element) fstNode;
NodeList fstNmElmntLst = fstElmnt.getElementsByTagName(childTags.get(count));
Element fstNmElmnt = (Element) fstNmElmntLst.item(0);
NodeList fstNm = fstNmElmnt.getChildNodes();
subItems.add(((Node) fstNm.item(0)).getNodeValue());
}
}
xmlMap.put(subItems, s);
}
} catch (SAXParseException err) {
System.out.println("** Parsing error" + ", line " + err.getLineNumber() + ", uri " + err.getSystemId());
System.out.println(" " + err.getMessage());

} catch (SAXException e) {
Exception x = e.getException();
((x == null) ? e : x).printStackTrace();

} catch (Throwable t) {
t.printStackTrace();
}
return xmlMap;
}
public static void main(String[] args) {
ParseXML p = new ParseXML();
String xmlData = "<data><row><Attribute_Name>java</Attribute_Name><VALUE>5656</VALUE><Child_Name>kids</Child_Name></row>"+
"</data>";
String rootTag = "row";
List<String> tagList = new ArrayList<String>();
tagList.add("Attribute_Name");
tagList.add("VALUE");
tagList.add("Child_Name");
Map<List<String>,Integer> myData = p.parseXMLData(xmlData, rootTag, tagList);
System.out.println(myData);
}
}

Android Dynamic List with buttons and event listener of each button

2010-11-02T10:54:00.000-07:00

Creating a custom list view – a custom layout, a custom row layout and how we bind the custom data holder to these layouts.

So, here we extends simple Activity not ListActivity.

Here i am giving the entire work of my Dynamic List with Button, where we get the event listener of each button from android:onClick="myClickHandler" in one of the layout file. From this event we can get the selected value and pass to other intents.

Here is the program....if you find any concerns or updates let me know will update accordingly....

package com.jit;
/*
* Vinay Guntaka
* Desc: Dynamic List with buttons and event listener of each buttons.
*/
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;

public class ListViewButtons extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ListView listView = (ListView)findViewById(R.id.btnOptionList);
        List<HashMap<String, String>> myOptList = getOptionList(EnumTypes.OPTION);
        SimpleAdapter optionList = new SimpleAdapter(getBaseContext(),myOptList,R.layout.btnstablerows,
                new String[]{
                "optnCard"
                },new int[]{
                R.id.btnAddOptn
        });
        listView.setAdapter(optionList);
        listView.setTextFilterEnabled(true);
    }
    /*    myClickHandler() is defined in btnstablerows.xml for
     * onClick event android:onClick="myClickHandler".
     */
    public void myClickHandler(View v)
    {
    LinearLayout vwParentRow = (LinearLayout)v.getParent();
    /*
     * Based on the row of each field the values of <td> can be
     * get based on the field type and field location
     * just replace with 0,1,2,.... of getChildAt();
     * get the 2nd child of our ParentRow (remember in java that arrays start with zero,
    * so our 2nd child has an index of 1)
     */
    Button btnChild = (Button)vwParentRow.getChildAt(0);
    Toast.makeText(getBaseContext(), btnChild.getText(), Toast.LENGTH_LONG).show();
    int c = Color.CYAN;
    vwParentRow.setBackgroundColor(c);
    vwParentRow.refreshDrawableState();
    Toast.makeText(getBaseContext(), "Hey event fired", Toast.LENGTH_LONG).show();

    }
    private ArrayList<HashMap<String, String>> getOptionList(EnumTypes type){
        ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
        HashMap<String, String> map = new HashMap<String, String>();
        switch (type) {
        case OPTION:
            map.put("optnCard", "JAVA");
            mylist.add(map);
            map = new HashMap<String, String>();
            map.put("optnCard", "Eclipse Galileo");
            mylist.add(map);
            map = new HashMap<String, String>();
            map.put("optnCard", "Android 2.2");
            mylist.add(map);
            map = new HashMap<String, String>();
            map.put("optnCard", "Simulator Android");
            mylist.add(map);
            break;

        default:
            break;
        }
        return mylist;
    }
    public enum EnumTypes{
        OPTION
    }
}

-----------------

main.xml

----------

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<ListView android:id="@+id/btnOptionList"
        android:layout_width="200px" android:layout_height="wrap_content"
        android:drawSelectorOnTop="false" android:paddingLeft="35px"
        android:paddingTop="10px" android:clickable="true" android:scrollbars="none"
        >
    </ListView>
</LinearLayout>

----------------

btnstablerows.xml

--------------

<?xml version="1.0" encoding="utf-8"?>
    
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:paddingTop="4dip" android:paddingBottom="6dip"
    android:layout_width="fill_parent" android:layout_height="wrap_content"

    >
    <Button android:id="@+id/btnAddOptn" android:layout_width="fill_parent"
        android:layout_height="wrap_content" android:clickable="true"     />
</LinearLayout>

-----------------------
Hey.., I am a newbie to Android World
So please have a look at my Program and let me know if any thing missing

Thanks

Android Environment setup with Eclispe3.5 Galileo

2010-11-02T10:34:00.000-07:00

Android Plugin Installation Procedure to Eclispe3.5 Galileo

Minimum requirements for developing a sample android application are as follows:

Java 1.6 Eclipse Galileo
Android SDK

You can download the Android SDK from the following link with respective OS :

http://developer.android.com/sdk/index.html

Install the ADT Plug-in for Eclipse:

If you are developing in Eclipse, set up a remote update site at https://dl-ssl.google.com/android/eclipse/.

Install the Android Development Tools (ADT) Plugin, restart Eclipse, and set the "Android" preferences in Eclipse to point to the SDK install location. For detailed instructions, see ADT Plugin for Eclipse.

Procedure for downloading plugins:

Start Eclipse, then select Help > Install New Software.

In the Available Software dialog, click Add....

In the Add Site dialog that appears, enter a name for the remote site (for example, "Android Plugin") in the "Name" field.In the "Location" field, enter this URL:
https://dl-ssl.google.com/android/eclipse/

Note: If you have trouble acquiring the plugin, you can try using "http" in the URL, instead of "https" (https is preferred for security reasons).

Click OK.

Back in the Available Software view, you should now see "Developer Tools" added to the list. Select the checkbox next to Developer Tools, which will automatically select the nested tools Android DDMS and Android Development Tools.

Click Next.In the resulting Install Details dialog, the Android DDMS and Android Development Tools features are listed.

Click Next to read and accept the license agreement and install any dependencies, then click Finish.Restart Eclipse.

So you are ready to develop the Android Programs

At first you have to set the Android RunTime :-

Goto Eclipse Window tab-> Preferences ->set the Android SDK location (downloaded of the Android sdk system path).

Android SDK and AVD Manger(Android Emulator):

After Successfull installation of Android plugins you can see a icon with a down arrow (i.e, Android SDK and AVD console)on click it opens the list of existing AVD (Android Virtual Device ) if not you can create a new AVD by selecting the New button.There you can give the AVD name and selecting the target as android version (1.5,2.1,2.2..,)In Hardware there are certain options that supports the Android Emulator.After giving all details mentioned you can start the Device by pressing Launch button to open the Android Emulator.

There is a DDMS(Dalvik Debug Monitoring Service) prespetive to open the LogCat of Android,FileExplorer view etc.,

The above process is to configure the Android Environment.

Thanks

The Evolution of Java

2010-10-28T11:14:00.000-07:00

The Evolution of JAVA

JDK 1.0 Intial Release

JDK 1.1

an extensive retooling of the AWT event model
Inner classes added to the language
JavaBeans
JDBC
RMI

J2SE 1.2

strictfp keyword
reflection which supports introspection only, no modification at runtime possible
The swing graphical API was integrated into the core classes
Sun's JVM was equipped with a JIT Compiler for the first time
Java aplug-in
Java IDL, and IDL Implementation for CORBA Interoperability.
Collection Framework

J2SE 1.3

HotSpot JVM Included
RMI was modified to support optional compatibilty with CORBA
JAvaSound
Java Naming and Directory inteface (JNDI) included in core libraries (previously available as an extension)
Java platform Debugger Architecture(JPDA)

J2SE 1.4

Assesrt Keyword
Regular expression modedled after perl regular expressions.
exception chaining allows an exception to encapsulate original/ lower-level exception
Internet protocal version (IPV6) support
non-blocking NIO (new input / output)
Logging API
Image I/O API for reading and writing images in formats like JPEG and PNG
Integrated XML parser and XSLT processor(JAXP)
Integrated Security and cryptography

J2SE 5.0

Generics
Metadata
Autoboxing / unboxing
Enumerations
Swing New skinnable look and feel, called synth
Varargs
Enchanced "for loop"
Fix the previously broken semantics of the java Memory model, which defines how threads interact through memory.
Automatic Stud generation for RMI objects

Java SE 6

Support for order win9x sessions dropped
Scripting Language Support (JSR 223)
Dramatic performance improvements for the core
platform and swing
Improved webservice support through JAX WS
JDBC 4.0 support
JAva compiler aPI
Upgrade of JAXB to version2.0
support for pluggable annotations
Many GUI improvements

Java SE7

JVM support for dynamic languages, following the prototyping work currently done on the Multi language virtual machine
A new library for parallel computing pn Multi core processors

The History of Java

2010-10-27T10:58:00.000-07:00

The History of JAVA

          Java is related to C++, which is a direct descendant of C. Much of the character of java is inherited from these two languages. From C, Java derives its Syntax. Many of java's Object-Oriented features were influenced by C++. In fact, several of Java's defining characteristics come from or are responses to its predecessors.

The Creation of JAVA

       Java was conceived by James Gosling, Patrick Naughton, Chris Warth, Ed Frank and Mike Sheridan at Sun Micro Systems, Inc in 1991. It took 18 moths to develop the first working version. The language was initially called "Oak" but was renamed "Java" in 1995. Between the initial implementation of Oak in the fall of 1992 and the public announcement of java in the spring of 1995, many more people contributed ti the design and evolution of the language. Bill joy, Arthur van Hoff, Jonathan Payne, Frank Yellin and Tim Lindholm were key contributors to the maturing of the original prototype.

Java's Magic: The Bytecode

     The key that allows Java to solve both the security and the portability problems just described in that the output of a Java compiler is not executable code. Rather it is bytecode. Bytecode is a highly optimized set of instructions designed to be executed by the Java run-time system, which is called Java Virtual Machine(JVM). In essence the original JVM was designed as an interpreted for bytecode.

The Java Buzzwords

Simple
Secure
Portable
Object-orinted
Robust
Multithreaded
Architecure-neutral
Interpreted
High performance
Distributed
Dynamic

Understanding OOP Concepts

2010-10-27T10:40:00.000-07:00

OOPs:

Classes--The "Blueprints" for an object and the actual code that defines the properties and methods.

Objects-- Running instances of a class that contain all the internal data and state information needed for your application to function.

Inheritance-- The ability to define a class of one kind as being a subtype of a different kind of class (much the same way a square is a kind of rectangle)

Polymorphism-- Allows a class to be defined as being a member of more than one category of classes (just a car is a "thing with an engine" and "a thing with wheels")

Interfaces-- A way of specifying that an object is capable of doing something without actually defining how it is to be done (e.g a dog and a human are "things that walk" but they do it very differently )

Encapsulation-- The ability of an object to project access to its internal data.