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Good News......

2010-02-20T00:40:00.000-08:00

Hello my Friends, if you would like to create your web and window based applications, Web site and ECommerce Applications, please contact with Unique IT Solutions Pte Ltd , go and view their services.

Java Training Session 2 (Introduction to the Java Programming Language)

2009-07-22T01:43:00.001-07:00

1. Key Concept of Java Programming

Sample Java Code
class FirstJava
{
public static void main(String args[ ]) // main Method()
{
System.out.println(“Hello World!”); // Display the output message
}
}

Java program will be start with the class and you can give the name of the class whatever you want. When you save the file, just give the file name using the class name. Eg. If you class name is FirstJava, you need to give file name in helloWorld.java. When you give the filename, you need to check where is the main method. If your class has main method, you can give the file name the same with the class name that have main method. All the program must have at least one main method().

Eg. You have two class.

class A
{

}
class B
{
public static void main(String args[])
{
//some code here
}
}

The file name should be B.Java.

Compilation Stage

C:\> cd \myfolder
C:\myfolder> dir
C:\myfolder> set path=%path%;C:\Program Files\Java\jdk1.6.0\bin
C:\myfolder> javac FirstJava.java
C:\myfolder> dir
C:\myfolder> java FirstJava

Output: Hello World!
(if you are not clear how to execute the program, please go to Session 1)

Theories and Concepts

1. Why is main() method static?

The method can be access directly with the help of ClassName. So when a program is started the jvm search for the class with main method and calls it without creating an object of the class.

2. What is the difference between static methods and instance methods?
Instance method belongs to the instance of a class therefore it requires an instance before it can be invoked, whereas static method belongs to the class itself and not to any class instance so it doesn’t need an instance to be invoked. Instance methods use dynamic (late) binding, whereas static methods use static (early) binding.

3. What is difference between abstract class and interface?

1) A class is called abstract when it contains at least one abstract method. It can also contain n numbers of concrete method.Interface can contain only abstract( non implemented) methods.

2) The abstract class can have public,private,protect or default variables and also constants. In interface the variable is by default public final. In nutshell the interface doesnt have any variables it only has constants.

3) A class can extend only one abstract class but a class can implement multiple interfaces.

4. Does Java has multiple inheritance?

Java doesnt support multiple inheritance but it provide a way through which it can enact it.

5. What are the different types of references in java?
types of references—soft, weak, and phantom references.
A SoftReference can be used to implement a cache. An object that is not reachable by a strong reference (that is, not strongly reachable), but is referenced by a soft reference is called softly reachable. A softly reachable object may be garbage collected at the discretion of the garbage collector. This generally means that softly reachable objects will only be garbage collected when free memory is low, but again, it is at the discretion of the garbage collector. Semantically, a soft reference means "keep this object unless the memory is needed."
A WeakReference is used to implement weak maps. An object that is not strongly or softly reachable, but is referenced by a weak reference is called weakly reachable. A weakly reachable object will be garbage collected during the next collection cycle. This behavior is used in the class java.util.WeakHashMap. A weak map allows the programmer to put key/value pairs in the map and not worry about the objects taking up memory when the key is no longer reachable anywhere else. Another possible application of weak references is the string intern pool. Semantically, a weak reference means "get rid of this object when nothing else references it."

A PhantomReference is used to reference objects that have been marked for garbage collection and have been finalized, but have not yet been reclaimed. An object that is not strongly, softly or weakly reachable, but is referenced by a phantom reference is called phantom reachable. This allows for more flexible cleanup than is possible with the finalization mechanism alone. Semantically, a phantom reference means "this object is no longer needed and has been finalized in preparation for being collected."

6. Java supports pass by value or pass by reference?
Java supports only pass by value. The arguments passed as a parameter to a method is mainly primitive data types or objects. For the data type the actual value is passed.
Java passes the references by value just like any other parameter. This means the references passed to the method are actually copies of the original references.Java copies and passes the reference by value, not the object.

7. What is memory leak?
A memory leak is where an unreferenced object that will never be used again still hangs around in memory and doesnt get garbage collected.

8. Can an abstract class have a static method?

Yes an abstract class have a static method and it can be accessed by any other class(even not a concrete class).

9. Can an abstract class have a constructor?

Yes an abstract class have a default and parameterized constructors.

10. Why static methods cannot access non static variables or methods?

A static method cannot access non static variables or methods because static methods doesnt need the object to be accessed. So if a static method has non static variables or non static methods which has instantiated variables they will no be intialized since the object is not created and this could result in an error.

11. What is the difference between final, finally and finalize() in Java?

final - constant declaration. A final variable act as constant, a final class is immutable and a final method cannot be ovrriden.

finally - handles exception. The finally block is optional and provides a mechanism to clean up regardless of what happens within the try block (except System.exit(0) call). Use the finally block to close files or to release other system resources like database connections, statements etc.

finalize() - method helps in garbage collection. A method that is invoked before an object is discarded by the garbage collector, allowing it to clean up its state. Should not be used to release non-memory resources like file handles, sockets, database connections etc because Java has only a finite number of these resources and you do not know when the garbage collection is going to kick in to release these non-memory resources through the finalize() method.

2. Introduction to Object Oriented Analysis Concept and basic Designing class (UML)

3. Developing and Testing Java Program

Discussion Topic 12 ( ADO.Net )

2009-07-14T00:21:00.000-07:00

A DataSet is a collection of DataTable
A DataTable is a collection of DataRow
A DataRow is a collection of data elements
A TableAdapter is a device that uses a hidden DataAdapter (which is based on a hidden DataReader) to fill a DataTable with DataRows from a data source such as a database, and send updates (changes to the DataRows) back to the data source TableAdapters do not fill DataSets. DataSets do not hold data directly.

In .NET 2.0 controls are usually bound to data through a BindingSource A BindingSource sits on top of a block of data (such as a DataTable) and maintains knowledge of position; changing the .Position of a BindingSource changes what row of data all controls that bind through that BindingSource, are looking at BindingSources can also filter and sort the rows they present, independently of the DataTable or DataRelation upon which they are based A DataRelation acts as a filter device to only show records from a child data source (usually a DataTable) whose foreign key matches the primary key of the current row of the relation's parent table. Because the concept of "Current Parent Row" is needed for a DataRelation to work, they are usually found within BindingSources; the Parent BindingSource exposes all the DataRelations whose parent table is the the table upon which the BindingSource sits.

A BindingNavigator is a device that alters the position of a BindingSource through use of its [|<], [<], [>] and [>|] buttons, and can be used to invoke common actions on the BindingSource, such as .AddNew(), .Delete() and .Update()

A DataReader is the only way data comes out of a database. Anything else is an additional device to fill the need for some functionality.

Discussion Topic 11 ( MVC Model )

2009-07-14T00:20:00.000-07:00

Model
-----
This is where your data is stored. The DataTable is the Model.

View
----
This is the component that shows the data found in the Model. The DataGridView is the View here. When used in data-bound mode, you dont copy from the datatable into the grid, the grid just shows what it finds in the Model. Change the Model, the View changes what it shows

Controller
----------
I mentioned changing the Model; that's what this does. Most of the time, the thing that changes the Model is the same thing that Views the Model. It doesnt really make sense (usually) to show some text from your database, in a Label, but then have a TextBox to edit it.. because the TextBox is capable of being the View.
But suppose you have a button called [Clear] that removes all the information from the Model. Pressing this button clears the Model and suddenly the View (grid) updates to show nothing. This is an example of a Controller; it affects the Model, but it doesnt behave as a View of anything in the Model.

MVC is a good OO concept. Put your data here, show it using that component there. "There" and "here" shouldnt be the same thing. Dont store your data into your View components.

<< Question and Answer Section >>

2009-07-10T00:04:00.001-07:00

Hi,

If you would like to ask something, please leave the question in the comment box and we will answer in next day. We always waiting for your IT related questions? If you want to hide your question, we will just drop the answer to your email.

Best Regards,
Admin (Unique Training Hub)

Java Training Session 1 ( Introduction )

2009-07-08T23:10:00.000-07:00

1. What is Java?

Ans : Java is a computer programming language. It is allow to write computer instructions using English based commands. It’s known as a “high-level” language because it can be read and written easily by humans. Java has a set of rules and regulations that determine how the instructions are written. These are known as its “syntax”. Once a program has been written, the high-level instructions are translated into numeric codes that computers can understand and execute.

2. How can we execute java program?

Ans: Run Command Prompt (found under All Programs/Accessories in the Start menu). Type

C:\> cd \myfolder

C:\myfolder> dir

C:\myfolder> set path=%path%;C:\Program Files\Java\jdk1.6.0\bin

C:\myfolder> javac filename.java

This runs javac.exe, the compiler. You should see nothing but the next system prompt...

C:\myfolder> dir

javac has created the filename.class file. You should see filename.java and filename.class among the files.

C:\myfolder> java filename

This runs the Java interpreter. You should see the program output:

Output

3. Advantages of Java Programming

Ans:
Java is simple:
--------------

Java was designed to be easy to use and is therefore easy to write, compile, debug, and learn than other programming languages. The reason that why Java is much simpler than C++ is because Java uses automatic memory allocation and garbage collection where else C++ requires the programmer to allocate memory and to collect garbage.

Java is object-oriented:
------------------------

Java is object-oriented because programming in Java is centered on creating objects, manipulating objects, and making objects work together. This allows you to create modular programs and reusable code.

Java is platform-independent:
----------------------------

One of the most significant advantages of Java is its ability to move easily from one computer system to another.

The ability to run the same program on many different systems is crucial to World Wide Web software, and Java succeeds at this by being platform-independent at both the source and binary levels.

Java is distributed:
-------------------

Distributed computing involves several computers on a network working together. Java is designed to make distributed computing easy with the networking capability that is inherently integrated into it.

Writing network programs in Java is like sending and receiving data to and from a file. For example, the diagram below shows three programs running on three different systems, communicating with each other to perform a joint task.

Java is interpreted:
--------------------

An interpreter is needed in order to run Java programs. The programs are compiled into Java Virtual Machine code called bytecode.

The bytecode is machine independent and is able to run on any machine that has a Java interpreter. With Java, the program need only be compiled once, and the bytecode generated by the Java compiler can run on any platform.

Java is secure:
---------------

Java is one of the first programming languages to consider security as part of its design. The Java language, compiler, interpreter, and runtime environment were each developed with security in mind.

Java is robust:
--------------

Robust means reliable and no programming language can really assure reliability. Java puts a lot of emphasis on early checking for possible errors, as Java compilers are able to detect many problems that would first show up during execution time in other languages.

Java is multithreaded:
---------------------

Multithreaded is the capability for a program to perform several tasks simultaneously within a program. In Java, multithreaded programming has been smoothly integrated into it, while in other languages, operating system-specific procedures have to be called in order to enable multithreading. Multithreading is a necessity in visual and network programming.

4. Type of java programming

Ans:
SE (Standard Edition)
EE (Enterprise Edition)
ME (Micro Edition)

5. What is java Byte Code?

Ans: Java bytecode is the form of instructions that the Java virtual machine executes. Each bytecode opcode is one byte in length, although some require parameters, resulting in some multi-byte instructions. Not all of the possible 256 opcodes are used. In fact, Sun Microsystems, the original creators of the Java programming language, the Java virtual machine and other components of the Java Runtime Environment (JRE), have set aside 3 values to be permanently unimplemented.

6. What is java Applet?

Ans: A Java applet is an applet that delivered to the users in the form of Java bytecode. Java applets can run in a Web browser using a Java Virtual Machine (JVM). Java applets were introduced in the first version of the Java language in 1995. Java applets are usually written in the Java programming language but they can also be written in other languages that compile to Java bytecode such as Jython.

7. Where can I get Java and Java IDE?

Ans: http://www.sun.com/download/index.jsp

Discussion Topic 10 (Exam Purpose)

2009-07-08T01:16:00.000-07:00

1. How can I practice my MCPD Framework 2.0 EXAM? Which one is the most suitable, Web, Window or Enterprise?

First, find Self-Paced training kits for relevant exam. Its target to the certification trend. Its very useful. If you want to get practice, please browse MSDN (http://msdn.microsoft.com) and you can learn the coding.

For the most suitable one is difficult to say which one is good and which one the bad because its depend on you preference. Eg. I like Web Programming, so I will say MCPD Web is better, on the other hand, MCPD window also useful. So, you need to decide which trend you want to take and your career path.

Good luck for all of your IT Certification exams...

Discussion Topic 9 (SQL)

2009-07-08T01:14:00.000-07:00

1. How to reduce the size of Transaction log DB? My Transaction Log DB size is very big, so what should I do?

First Open MSSQL Server Management Studio, then, switch the DB Recovery mode to "Simple",

Then following procedure should do -

1. Locate your database, and right click on it
2. Select "Properties"
3. On the left pane, select "Options"
4. On the right pane, select "Simple" from the "Recovery Model" dropdown list.
5. Click "Ok"

Then Click New Query and type the following query -

CHECKPOINT;
DBCC SHRINKFILE ('databasename_log');
databasename_log is the actual file name of the transaction log for your selected database on the filesystem that you want to shink. No path needed.

Its will be Ok for all. Try you best.

Discussion Topic 8 (C#)

2009-07-08T01:13:00.000-07:00

1. How can we use Delegate in C#?

A delegate in C# is similar to C++ pointer. Its allows the programmer to encapsulate a reference to a method inside a delegate object. The delegate object can then be passed to code which can call the referenced method, without having to know at compile time which method will be invoked.The basic Delegate has -

* result-type
* identifier
* parameters

public delegate void myDelegate ()

This declaration defines a delegate named myDelegate, which will encapsulate any method that takes no parameters and returns no value.

Discussion Topic 7 (Java)

2009-07-01T01:13:00.000-07:00

1. What is InitialContext and SessionContext?

a. InitialContext

The initial context implements the Context interface and provides the starting point for
resolution of names. When the initial context is constructed, its environment is initialized
with properties defined in the environment parameter passed to the constructor, and in any
application resource files. In addition, a small number of standard JNDI properties may be
specified as system properties or as applet.

b. SessionContext

The SessionContext interface provides access to the runtime session context that the
container provides for a session enterprise Bean instance. The container passes the essionContext interface to an instance after the instance has been created. The session context remains associated with the instance for the lifetime of the instance.

Discussion Topic 6 (General)

2009-07-01T01:12:00.000-07:00

1. What is Manifest file?

The manifest is a special file that can contain information about the files packaged in a JAR file. By tailoring this "meta" information that the manifest contains, you enable the JAR file to be used for a variety of purposes.

Pre-existing manifest file whose name: value pairs are to be included in MANIFEST.MF in the jar file. The m option and filename manifest are a pair -- if either is present, they must both appear. The letters m and f must appear in the same order that manifest and jarfile
appear.

Discussion Topics 5 (Java)

2009-06-26T20:54:00.000-07:00

1. What is Narrowing in Java?

Narrowing is the “exotic casting” needed for stub objects that come from a method that does not return the stub’s client interface. Since the JNDI lookup returns type Object, the object returned from the lookup must be narrowed to the bean’s home interface, and the cast to the bean’s home interface.

Narrowing is required for IIOP stubs (IIOP is the wire protocol for CORBA), because what’s returned from the lookup might not be capable of implementing multiple interfaces, and thus would know only about the methods in type Object. - Narrowing returns an object that implements the home interface.

The home interface extends EJBHome, which has four additional methods the client can see: getEJBMetaData(), getHomeHandle(), remove(Handle h), remove(Object primaryKey). The remove(Object primaryKey) must not be called on a session bean.

Discussion Topic 4 (Web Programming)

2009-06-25T06:18:00.001-07:00

1. What is caching in web application?

You can cache your application data by using the cache class. The instance of this class is private to each application. The life time of this class is the life time of the application itself. The cache object is recreated each time the application is restarted. The cache object is global, means the data stored in it is available anywhere within the web application, and in this regard this is similar to the application object. The difference between the cache object and the application object is that the cache object has some more powerful features that allows you to control the cached data.

With the cache object, each item or data stored in the cache object can have its priority state, and can have an expiration time. The Cache object uses those two features in situation like this: When your system's memory becomes scarce, the cache object chooses items with low priority or seldom use to remove and this frees memory. This is how the cache object ensures that unnecessary items does not consume valuable server resources.

Discussion Topic 3 (Java)

2009-06-25T05:00:00.000-07:00

1. What is stateless and stateful session bean?

Stateful
========

A stateful session bean is an enterprise bean (EJB component) that acts as a server-side extension of the client that uses it. The stateful session bean is created by a client and will work for only that client until the client connection is dropped or the bean is explicitly removed.
The stateful session bean is EJB component that implements the javax.ejb.SessionBean interface and is deployed with the declarative attribute "stateful". Stateful session beans are called "stateful" because they maintain a conversational state with the client. In other words, they have state or instance fields that can be initialized and changed by the client with each method invocation. The bean can use the conversational state as it process business methods invoked by the client.
Stateful session beans are usually developed to act as agents for the client, managing the interaction of other beans and performing work on behalf of the client application. An example is a shopping cart stateful session bean that tracks a client's product choices and can execute a sale when requested. Below is partial example of a stateful session bean that is used as a shopping cart.

Stateless
=========

A stateless session bean is an enterprise bean (EJB component) that provides a stateless service to the client. Conceptually, the business methods on a stateless session bean are similar to procedural applications or static methods; there is no instance state, so all the data needed to execute the method is provided by the method arguments.
The stateless session bean is an EJB component that implements the javax.ejb.SessionBean interface and is deployed with the declarative attribute "stateless". Stateless session beans are called "stateless" because they do not maintain conversational state specific to a client session. In other words, the instance fields in a stateless session bean do not maintain data relative to a client session. This makes stateless session beans very lightweight and fast, but also limits their behavior.
Stateless session beans are usually developed as a set of related and simple services. Think of a session bean as a functional API where each business method represents an isolated independent service. An example is a CreditService bean that provides methods for making charges against different types of credit cards (MC, Visa, Discovery, etc).

Discussion Topic 2 (MS Programming)

2009-06-20T18:05:00.000-07:00

1. Difference between DataSet and RecordSet?

Dataset can represent an entire relational databaes in menory, complete with tables, relations and views. Also can retrieve data from Oracle and SQL Server.

Recordset cannot be transmitted on HTTP while Dataset can be.

Discussion Topic 1 (Java )

2009-06-20T17:52:00.000-07:00

1. What is the purpose for using Serialization?

Serializable is a marker interfaces that tells the JVM is can write out the state of the object to some stream (basically read all the members, and write out their state to a stream, or to disk or something). The default mechanism is a binary format. You can also use it to clone things, or keep state between invocations, send objects across the network etc.

Career Development Section

2009-06-20T17:29:00.000-07:00

1. Senior System Analyst (SAP)
Salary: S$5,000

Responsibilties:

Responsible for performing system analysis, design, programming, testing and implementation of appropriate solutions to support the SAP Financial system
Work closely with end users to gather and understand their requirements, propose business solutions and enhance the system

Job Requirements:

At least a Degree in IT, Computing, Computer Science or related fields
Minimum 4 - 5 years of experience in related positions Strong experience in the implementation, maintenance, testing of the following SAP modules (FI/CO/RE/PCA/CFM, and SD and MM) Experience in ABAP programming is advantageous At least undergone 1 - 2 full cycles of SAP implementations Good communication and interpersonal skills
Interested candidates, please send your resumes in MS Word format to bryanong@recruitexpress.com.sg.

2. IT Executive (System/Network)

Salary: Negotiable

Job Requirements:

* Minimum Diploma or Degree in IT, Computer Science, Computing or equivalent
* Good relevant working experience of at least 1 - 5 years (Various positions available)
* Experience with Windows based Wintel or Unix Servers administration preferred
* Good technical knowledge and working experience in Network management and support (LAN/WAN, VPN, Routing and Switching)
* Professional certifications is an advantage (MCSA, MCSE or CCNA, CCNP)
* Singaporeans or Singapore P.R.s preferred

Fresh Dipolma/Degree holders are welcome to apply

Interested applicants, please send your resumes in MS Word format to bryanong@recruitexpress.com.sg and attention to "Will Chen" in the Subject Title.

Daily Assignment for SCJP Exam ...

2009-06-20T11:43:00.000-07:00

Question (1)

abstract class ab

{ abstract private void smile();

}

class test extends ab

{ public static void main(String[] args)

{

test inst_test = new test();

}

a. Compile with warnings indicating smile() should be public.

b. Compiles without warnings.

c. Compiles with warnings indicating smile() is not inherited.

d. Compile error

e. Runtime Exception.

Reference :

Answer: d.Compile error. abstract methods cant be private.

Question (2)

If two instances, test_one and test_two of Serializable class test are written to a file named “serial.serial” in that order, which of the following are true ?

When reading back from the file, test_two is the first object that is read.
When reading back from the file, test_one is the first object that is read.
The object cannot be read from a file named “serial.serial”.
None of the above.

Reference:
Answer: b. test_one will be the first object to be read from the file

Question (3)

class test

{

public static void main ( String [] args )

{

final Integer x4 = 8;

final int x = 10;

switch ( x )

{

case x4:

System.out.println("4");

break;

case x:

System.out.println("x");

break;

}

Compile error
Runtime error
Prints x
Prints 4

None of the above

Reference

Answer: a Compile error. Final objects are not allowed in a case statement. A final object’s value can be changed whereas a final variables value cannot be changed.

Preparation for SCJP Exam .....

2009-06-20T11:29:00.000-07:00

You can find the resources and ebooks from online. If you want to take this exam, please focus on the following topics -

Declarations, Initialization and Scoping
Flow Control
API Contents
Concurrency
OO Concepts
Collections / Generics
Fundamentals

There are many web sites for SCJP Preparation. These are a few, www.javaranch.com
http://sun.java.com You can download the ebook from www.esnips.com which is a file share site.

It can take at least 3 months to longer up to your study time and prior knowledge in programming. I'm also preparing for it. I use SCJP 5 written by Kathy Sierra, a very good book, but you will need a foundation of java programming before reading it.

If you are beginner, try to read a book of foundation of Java Programming first, then try a preparation book like the one I recommended.

If you want to prepare for SCJP, please learn SL-110 and SL-275 from SUN Microsystem course. Besides, Sun Certified Programmer for Java exam guide which has written by Kathy Sierra will help u alot to pass the exam because it was written for the exam purpose. I can gurantee it because i've got SCJP Certificate by reading it and doing some other learning and being guided by my sub leader.