Java (programming language)

Is Java “pass-by-reference” or “pass-by-value”?

2021-03-22T03:37:00.003-07:00

Java is always pass-by-value.

Unfortunately, we never handle an object at all, instead juggling object-handles called references _{^{(which are passed by value of course)}}. The chosen terminology and semantics easily confuse many beginners.

It goes like this:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

    // we pass the object to foo
    foo(aDog);
    // aDog variable is still pointing to the "Max" dog when foo(...) returns
    aDog.getName().equals("Max"); // true
    aDog.getName().equals("Fifi"); // false
    aDog == oldDog; // true
}

public static void foo(Dog d) {
    d.getName().equals("Max"); // true
    // change d inside of foo() to point to a new Dog instance "Fifi"
    d = new Dog("Fifi");
    d.getName().equals("Fifi"); // true
}


In the example above aDog.getName() will still return "Max". The value aDog within main is not changed in the function foo with the Dog "Fifi" as the object reference is passed by value. If it were passed by reference, then the aDog.getName() in main would return "Fifi" after the call to foo.
Likewise:
public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

    foo(aDog);
    // when foo(...) returns, the name of the dog has been changed to "Fifi"
    aDog.getName().equals("Fifi"); // true
    // but it is still the same dog:
    aDog == oldDog; // true
}

public static void foo(Dog d) {
    d.getName().equals("Max"); // true
    // this changes the name of d to be "Fifi"
    d.setName("Fifi");
}
In the above example, Fifi is the dog's name after call to foo(aDog) because the object's name was set inside of foo(...). Any operations that foo performs on d are such that, for all practical purposes, they are performed on aDog, but it is not possible to change the value of the variable aDog itself.

Struts interview questions 10

2012-05-05T02:38:00.000-07:00

Q:	What is ActionForm?
A:	An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm. ActionForm maintains the session state for web application and the ActionForm object is automatically populated on the server side with data entered from a form on the client side.

Q:	What is Struts Validator Framework?
A:	Struts Framework provides the functionality to validate the form data. It can be use to validate the data on the users browser as well as on the server side. Struts Framework emits the java scripts and it can be used validate the form data on the client browser. Server side validation of form can be accomplished by sub classing your From Bean with DynaValidatorForm class. The Validator framework was developed by David Winterfeldt as third-party add-on to Struts. Now the Validator framework is a part of Jakarta Commons project and it can be used with or without Struts. The Validator framework comes integrated with the Struts Framework and can be used without doing any extra settings.

Q:	Give the Details of XML files used in Validator Framework?
A:	The Validator Framework uses two XML configuration files validator-rules.xml and validation.xml. The validator-rules.xml defines the standard validation routines, these are reusable and used in validation.xml. to define the form specific validations. The validation.xml defines the validations applied to a form bean.

Q:	How you will display validation fail errors on jsp page?
A:	Following tag displays all the errors: <html:errors/>

Q:	How you will enable front-end validation based on the xml in validation.xml?
A:	The <html:javascript> tag to allow front-end validation based on the xml in validation.xml. For example the code: <html:javascript formName=\"logonForm\" dynamicJavascript=\"true\" staticJavascript=\"true\" /> generates the client side java script for the form \"logonForm\" as defined in the validation.xml file. The <html:javascript> when added in the jsp file generates the client site validation script.

Q:	How to get data from the velocity page in a action class?
A:	We can get the values in the action classes by using data.getParameter(\"variable name defined in the velocity page\")

Struts interview questions 9

2012-05-05T02:35:00.000-07:00

Q:	What is Struts?
A:	The core of the Struts framework is a flexible control layer based on standard technologies like Java Servlets, JavaBeans, ResourceBundles, and XML, as well as various Jakarta Commons packages. Struts encourages application architectures based on the Model 2 approach, a variation of the classic Model-View-Controller (MVC) design paradigm. Struts provides its own Controller component and integrates with other technologies to provide the Model and the View. For the Model, Struts can interact with standard data access technologies, like JDBC and EJB, as well as most any third-party packages, like Hibernate, iBATIS, or Object Relational Bridge. For the View, Struts works well with JavaServer Pages, including JSTL and JSF, as well as Velocity Templates, XSLT, and other presentation systems. The Struts framework provides the invisible underpinnings every professional web application needs to survive. Struts helps you create an extensible development environment for your application, based on published standards and proven design patterns.

Q:	What is Jakarta Struts Framework?
A:	Jakarta Struts is open source implementation of MVC (Model-View-Controller) pattern for the development of web based applications. Jakarta Struts is robust architecture and can be used for the development of application of any size. Struts framework makes it much easier to design scalable, reliable Web applications with Java.

Q:	What is ActionServlet?
A:	The class org.apache.struts.action.ActionServlet is the called the ActionServlet. In the the Jakarta Struts Framework this class plays the role of controller. All the requests to the server goes through the controller. Controller is responsible for handling all the requests.

Q:	How you will make available any Message Resources Definitions file to the Struts Framework Environment?
A:	T Message Resources Definitions file are simple .properties files and these files contains the messages that can be used in the struts project. Message Resources Definitions files can be added to the struts-config.xml file through <message-resources /> tag. Example: <message-resources parameter=\"MessageResources\" />.

Q:	What is Action Class?
A:	The Action Class is part of the Model and is a wrapper around the business logic. The purpose of Action Class is to translate the HttpServletRequest to the business logic. To use the Action, we need to Subclass and overwrite the execute() method. In the Action Class all the database/business processing are done. It is advisable to perform all the database related stuffs in the Action Class. The ActionServlet (commad) passes the parameterized class to Action Form using the execute() method. The return type of the execute method is ActionForward which is used by the Struts Framework to forward the request to the file as per the value of the returned ActionForward object.

Struts interview questions 8

2012-05-05T02:32:00.000-07:00

36.What are differences between <bean:message> and <bean:write>

<bean:message>: is used to retrive keyed values from resource bundle. It also supports the ability to include parameters that can be substituted for defined placeholders in the retrieved string.

<bean:message key="prompt.customer.firstname"/>

<bean:write>: is used to retrieve and print the value of the bean property. <bean:write> has no body.

<bean:write name="customer" property="firstName"/>

37.How the exceptions are handled in struts?

Exceptions in Struts are handled in two ways:

Programmatic exception handling :

Explicit try/catch blocks in any code that can throw exception. It works well when custom value (i.e., of variable) needed when error occurs.

Declarative exception handling :You can either define <global-exceptions> handling tags in your struts-config.xml or define the exception handling tags within <action></action> tag. It works well when custom page needed when error occurs. This approach applies only to exceptions thrown by Actions.

<global-exceptions>
<exception key="some.key"
type="java.lang.NullPointerException"
path="/WEB-INF/errors/null.jsp"/>
</global-exceptions>

38.What is difference between ActionForm and DynaActionForm?

An ActionForm represents an HTML form that the user interacts with over one or more pages. You will provide properties to hold the state of the form with getters and setters to access them. Whereas, using DynaActionForm there is no need of providing properties to hold the state. Instead these properties and their type are declared in the struts-config.xml
The DynaActionForm bloats up the Struts config file with the xml based definition. This gets annoying as the Struts Config file grow larger.
The DynaActionForm is not strongly typed as the ActionForm. This means there is no compile time checking for the form fields. Detecting them at runtime is painful and makes you go through redeployment.
ActionForm can be cleanly organized in packages as against the flat organization in the Struts Config file.
ActionForm were designed to act as a Firewall between HTTP and the Action classes, i.e. isolate and encapsulate the HTTP request parameters from direct use in Actions. With DynaActionForm, the property access is no different than using request.getParameter( .. ).
DynaActionForm construction at runtime requires a lot of Java Reflection (Introspection) machinery that can be avoided.

39.How can we make message resources definitions file available to the Struts framework environment?

We can make message resources definitions file (properties file) available to Struts framework environment by adding this file to struts-config.xml.

<message-resources parameter="com.login.struts.ApplicationResources"/>

40.What is the life cycle of ActionForm?

The lifecycle of ActionForm invoked by the RequestProcessor is as follows:

Retrieve or Create Form Bean associated with Action
"Store" FormBean in appropriate scope (request or session)
Reset the properties of the FormBean
Populate the properties of the FormBean
Validate the properties of the FormBean

Pass FormBean to Action

Struts interview questions 7

2012-05-05T02:27:00.000-07:00

31.What is DynaActionForm?

A specialized subclass of ActionForm that allows the creation of form beans with dynamic sets of properties (configured in configuration file), without requiring the developer to create a Java class for each type of form bean.

32.What are the steps need to use DynaActionForm?

Using a DynaActionForm instead of a custom subclass of ActionForm is relatively straightforward. You need to make changes in two places:

In struts-config.xml: change your <form-bean> to be an org.apache.struts.action.DynaActionForm instead of some subclass of ActionForm

<form-bean name="loginForm"type="org.apache.struts.action.DynaActionForm" >
<form-property name="userName" type="java.lang.String"/>
<form-property name="password" type="java.lang.String" />
</form-bean>

In your Action subclass that uses your form bean:

import org.apache.struts.action.DynaActionForm
downcast the ActionForm parameter in execute() to a DynaActionForm
access the form fields with get(field) rather than getField()

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;

import org.apache.struts.action.DynaActionForm;

public class DynaActionFormExample extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response)
            throws Exception {
DynaActionForm loginForm = (DynaActionForm) form;
                ActionMessages errors = new ActionMessages();
        if (((String) loginForm.get("userName")).equals("")) {
            errors.add("userName", new ActionMessage(
                            "error.userName.required"));
        }
        if (((String) loginForm.get("password")).equals("")) {
            errors.add("password", new ActionMessage(
                            "error.password.required"));
        }
        ...........

33.How to display validation errors on jsp page?

<html:errors/> tag displays all the errors. <html:errors/> iterates over ActionErrors request attribute.

34.What are the various Struts tag libraries?

The various Struts tag libraries are:

HTML Tags
Bean Tags
Logic Tags
Template Tags
Nested Tags
Tiles Tags

35.What is the use of <logic:iterate>?

<logic:iterate> repeats the nested body content of this tag over a specified collection.

Struts interview questions 6

2012-05-05T02:23:00.000-07:00

26.What is LookupDispatchAction?

The LookupDispatchAction is a subclass of DispatchAction. It does a reverse lookup on the resource bundle to get the key and then gets the method whose name is associated with the key into the Resource Bundle.

27.What is the use of LookupDispatchAction?

LookupDispatchAction is useful if the method name in the Action is not driven by its name in the front end, but by the Locale independent key into the resource bundle. Since the key is always the same, the LookupDispatchAction shields your application from the side effects of I18N.

28.What is difference between LookupDispatchAction and DispatchAction?

The difference between LookupDispatchAction and DispatchAction is that the actual method that gets called in LookupDispatchAction is based on a lookup of a key value instead of specifying the method name directly.

29.What is SwitchAction?

The SwitchAction class provides a means to switch from a resource in one module to another resource in a different module. SwitchAction is useful only if you have multiple modules in your Struts application. The SwitchAction class can be used as is, without extending.

30.What if <action> element has <forward> declaration with same name as global forward?

In this case the global forward is not used. Instead the <action> element’s <forward>takes precendence.

Struts interview questions 5

2012-05-04T06:11:00.000-07:00

21.What is DispatchAction?

The DispatchAction class is used to group related actions into one class. Using this class, you can have a method for each logical action compared than a single execute method. The DispatchAction dispatches to one of the logical actions represented by the methods. It picks a method to invoke based on an incoming request parameter. The value of the incoming parameter is the name of the method that the DispatchAction will invoke.

22.How to use DispatchAction?

To use the DispatchAction, follow these steps :

Create a class that extends DispatchAction (instead of Action)
In a new class, add a method for every function you need to perform on the service – The method has the same signature as theexecute() method of an Action class.
Do not override execute() method – Because DispatchAction class itself provides execute() method.
Add an entry to struts-config.xml

23.What is the use of ForwardAction?

The ForwardAction class is useful when you’re trying to integrate Struts into an existing application that uses Servlets to perform business logic functions. You can use this class to take advantage of the Struts controller and its functionality, without having to rewrite the existing Servlets. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page. By using this predefined action, you don’t have to write your own Action class. You just have to set up the struts-config file properly to use ForwardAction.

24.What is IncludeAction?

The IncludeAction class is useful when you want to integrate Struts into an application that uses Servlets. Use the IncludeAction class to include another resource in the response to the request being processed.

25.What is the difference between ForwardAction and IncludeAction?

The difference is that you need to use the IncludeAction only if the action is going to be included by another action or jsp. UseForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page.

Struts interview questions 4

2012-05-04T06:09:00.000-07:00

16.Can we have more than one struts-config.xml file for a single Struts application?

Yes, we can have more than one struts-config.xml for a single Struts application. They can be configured as follows:

<servlet>
<servlet-name>action</servlet-name>
<servlet-class>
        org.apache.struts.action.ActionServlet
</servlet-class>
<init-param>
<param-name>config</param-name>
  <param-value>
     /WEB-INF/struts-config.xml,
     /WEB-INF/struts-admin.xml,
     /WEB-INF/struts-config-forms.xml
  </param-value>
</init-param>
.....
<servlet>

17.What is the directory structure of Struts application?

The directory structure of Struts application :

18.What is the difference between session scope and request scope when saving formbean ?

when the scope is request,the values of formbean would be available for the current request.
when the scope is session,the values of formbean would be available throughout the session.

19.What are the important tags of struts-config.xml ?

The five important sections are:

20.What are the different kinds of actions in Struts?

The different kinds of actions in Struts are:

ForwardAction
IncludeAction
DispatchAction
LookupDispatchAction
SwitchAction

Struts interview questions 3

2012-05-04T06:05:00.000-07:00

11.What is ActionMapping?

Action mapping contains all the deployment information for a particular Action bean. This class is to determine where the results of the Action will be sent once its processing is complete.

12.How is the Action Mapping specified ?

We can specify the action mapping in the configuration file called struts-config.xml. Struts framework creates ActionMappingobject from <ActionMapping> configuration element of struts-config.xml file

<action-mappings>
<action path="/submit"
        type="submit.SubmitAction"
        name="submitForm"
        input="/submit.jsp"
        scope="request"
         validate="true">
<forward name="success" path="/success.jsp"/>
<forward name="failure" path="/error.jsp"/>
</action>
</action-mappings>

13.What is role of Action Class?

An Action Class performs a role of an adapter between the contents of an incoming HTTP request and the corresponding business logic that should be executed to process this request.

14.In which method of Action class the business logic is executed ?

In the execute() method of Action class the business logic is executed.

public ActionForward execute(
            ActionMapping mapping,
           ActionForm form,
             HttpServletRequest request,
          HttpServletResponse response)
          throws Exception ;

execute() method of Action class:

Perform the processing required to deal with this request
Update the server-side objects (Scope variables) that will be used to create the next page of the user interface
Return an appropriate ActionForward object

15.What design patterns are used in Struts?

Struts is based on model 2 MVC (Model-View-Controller) architecture. Struts controller uses the command design pattern and the action classes use theadapter design pattern. The process() method of the RequestProcessor uses the template method design pattern. Struts also implement the following J2EE design patterns.

Service to Worker
Dispatcher View
Composite View (Struts Tiles)
Front Controller
View Helper
Synchronizer Token

Struts interview questions 2

2012-05-04T06:03:00.000-07:00

6.What is ActionServlet?

ActionServlet is a simple servlet which is the backbone of all Struts applications. It is the main Controller component that handles client requests and determines which Action will process each received request. It serves as an Action factory – creating specific Action classes based on user’s request.

7.What is role of ActionServlet?

ActionServlet performs the role of Controller:

Process user requests
Determine what the user is trying to achieve according to the request
Pull data from the model (if necessary) to be given to the appropriate view,
Select the proper view to respond to the user
Delegates most of this grunt work to Action classes
Is responsible for initialization and clean-up of resources

8.What is the ActionForm?

ActionForm is javabean which represents the form inputs containing the request parameters from the View referencing the Action bean.

9.What are the important methods of ActionForm?

The important methods of ActionForm are : validate() & reset().

10.Describe validate() and reset() methods ?

validate() : Used to validate properties after they have been populated; Called before FormBean is handed to Action. Returns a collection of ActionError as ActionErrors. Following is the method signature for the validate() method.

public ActionErrors validate(ActionMapping mapping,HttpServletRequest request)

reset(): reset() method is called by Struts Framework with each request that uses the defined ActionForm. The purpose of this method is to reset all of the ActionForm's data members prior to the new request values being set.

public void reset() {}

Struts interview questions 1

2012-05-04T06:01:00.000-07:00

1.What is MVC?

Model-View-Controller (MVC) is a design pattern put together to help control change. MVC decouples interface from business logic and data.

Model : The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller.

View: The view provides the presentation of the model. It is the look of the application. The view can access the model getters, but it has no knowledge of the setters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur.

Controller:The controller reacts to the user input. It creates and sets the model.

2.What is a framework?

A framework is made up of the set of classes which allow us to use a library in a best possible way for a specific requirement.

3.What is Struts framework?

Struts framework is an open-source framework for developing the web applications in Java EE, based on MVC-2 architecture. It uses and extends the Java Servlet API. Struts is robust architecture and can be used for the development of application of any size. Struts framework makes it much easier to design scalable, reliable Web applications with Java.

4.What are the components of Struts?

Struts components can be categorize into Model, View and Controller:

Model: Components like business logic /business processes and data are the part of model.
View: HTML, JSP are the view components.
Controller: Action Servlet of Struts is part of Controller components which works as front controller to handle all the requests.

5.What are the core classes of the Struts Framework?

Struts is a set of cooperating classes, servlets, and JSP tags that make up a reusable MVC 2 design.

JavaBeans components for managing application state and behavior.
Event-driven development (via listeners as in traditional GUI development).
Pages that represent MVC-style views; pages reference view roots via the JSF component tree.

JAVA interview questions 37

2012-05-02T08:28:00.000-07:00

Q361. Explain about LinkedHashMap?
It is child class of HashMap. It is exactly same as HashMap except the following difference. In the case of HashMap the insertion order is not preserved but in the case of LinkedHashMap insertion order is preserved. Introduced in 1.4 version

Q362. What is IdentityHashMap?
It is exactly same as HashMap except the following difference.
In the HashMap JVM uses equals() method to identify duplicate keys but in the case of IdentityHashMap JVM uses == operator for this.

Q363. What is WeakHashMap?
It is exactly same as HashMap except the following difference.
In case of HashMap an Object is not eligible for garbage collection if it is associated with
HashMap even though it dosent have any external references. ie HashMap dominates garbage collector.
But in case of WeakHashMap , if an Object is not having any external references then it is always eligible for garabage collectoion even though it is associated with weakHashMap. ie garbage collector dominates WeakHashMap

Q364. What is TreeMap?
TreeMap can be used to store a group of objects as key-value pairs where all the entries are arranged according to some sorting order of keys.
The underlying data structure is RED-BLACK Tree
Duplicates keys are not allowed but values can be duplicated.
Insertion order is not preserved because insertion is based on some sorting order
If we are depending on Natural sorting order then keys should be homogeneous(violation leads to ClassCastException) but values need not homogeneous
In case of customized sorting order we can insert heterogeneous keys and values
For empty TreeMap as first entry with null values are allowed but after inserting that entry if we are trying to insert any other entry we will get NullPointerException For non empty TreeMap if we are trying to insert null keys we will get
NullPointerException
There are no restrictions for null values.

Q365. What is Hashtable?
Hashtable is a legacy Map and can be used to store objects as key value pairs.
The underlying data sturucture is Hashtabe
Duplicates keys are not allowed but duplicate values are allowed null insertion is not possible for both keys and values
all methods are synchronized
insertion order is not preserved because it is based on hashcode of keys heterogeneous Objects are allowed for both keys and values
introduced in 1.0 version it is legacy class

Q367. What is PriorityQueue?
It represents a data structure to hold group of individual objects prior to processing based on
some priority .it can be natural sorting order and it can be customized sorting order described by Comparator.
It is the implementation class of Queue interface.
Insertion order is not preserved because here insertion is done based on some sorting order
Duplicates are not allowed
null insertion is not possible even as first element also
If we are depending on natural sorting order Objects should be homogeneous violation leads to ClassCastException
If we are depending on customized sorting order Objects can be heterogeneous also.

Q368. What is Arrays class?
It is utility class for arrays.
It defines several utility methods for arrays like sorting an array or searching an element in array
present in java.util package

Q369. We are planning to do an indexed search in a list of objects. Which of the two Java collections should you use: ArrayList or LinkedList?
ArrayList

Q370. Why ArrayList is faster than Vector?
All methods present in the Vector are synchronized and hence any method can be executed by only one thread at a time. It slows down the execution.
But in ArrayList, no method is synchronized and hence multiple thread are allowed execute simultaneously which speed up the execution.

JAVA interview questions 36

2012-05-02T08:21:00.000-07:00

Q351. What is relation between ListIterator and Iterator?
ListIterator is child interface of Iterator

Q352. Explain about HashSet class?
The underlying data structure is Hashtable null values are accepted
duplicates are not allowed
insertion order is based on hashcode of the object hence insertion order is not preserved best suitable if frequent operation is search operations
HashSet class implements Serializable and Cloneable it is implementation class for Set interface
heterogeneous objects are allowed
it is introduced in 1.2 version

Q353. If we are trying to insert duplicate values in Set what will happen?
If we are trying to insert duplicate objects to the HashSet , we wont get any compile time or run time errors just the add(Object o) returns false and it doesn’t add that object.

Q354. What is LinkedHashSet?
It is the child class of HashSet. The main difference between HashSet and LinkedHashSet is: In the case of HashSet insertion order is not preserved , but in the case of LinkedHashSet insertion will be preserved.

Q355. What are major enhancements in 1.4 version of collection frame work?
LinkedHashSet
LinkedHashMap
IdentityHashMap

Q356. Explain about TreeSet?
It is Collection object which can be used to represent a group of objects according to some sorting order.
The underlying datastructure is Balanced tree Duplicates are not allowed
All objects are stored according to some sorting order hence insertion order is not preserved
Heterogeneous objects are not allowed violation leads to ClassCastException
For an Empty TreeSet as firs element null value can be inserted but after inserting that first value if we are trying to insert any other objects then we will get NullPointerException
For an non empty TreeSet if we are trying to inser null value at run time u will get NullPointerException

Q357. What is Comparable interface?
This interface can be used for defining natural sorting order of the objects. It is present in java.lang package
It contains a method public int compareTo(Object obj1)

Q358. What is Comparator interface?
This interface can be used for implementing customized sorting order. It is present in java.util package
It contains two methods
o public int compare(Object ,Object) o public boolean equals(Object)

Q359. What is Entry interface?
It is inner interface of Map.
In the Map each key value pair is considered as Entry object.
interface Map{
//more code here
interface Entry{
Object getKey()
Object getValue()
Object setValue(Object new)
}
}

Q360. Explain about HashMap?
It is a Map Object which can be used used to represent a group of objects as key-value pairs.
The underlying data structure is Hashtable
Duplicaes keys are not allowed duplicate values are allowed
Insertion order is not preserved because insertion is based on hashcode of keys. Heterogeneous objects are allowed for both keys and values
null key is allowed only once
null values are allowed multiple times
Introduced in 1.2 version

JAVA interview questions 35

2012-05-01T05:26:00.001-07:00

Q341. Explain about ArrayList class?
ArrayList is a Collection which can be used to represent a group of objects as a single entity.
it is a implemented class for List interface
Introduced in 1.2 version
The underlying data structure is resizable or growable array. Insertion order is preserved
Duplicates are allowed
Heterogeneous objects are allowed
null insertion is possible
This class implements RandomAccess , Serializable , Cloneable interfaces
Best choice for retrieval purpose and worst if our frequent operation is insertion or deletion in the middle

Q342. What is RandomAccess Interface?
If a collection class implements RandomAccess interface then we can access any of its element with the same speed.
RandomAccess interface is marker interface and it dosent contains any methods. ArrayList and vector classes implements this interface.

Q343. Explain about LinkedList class?
LinkedList is a Collection implemented class which can be used for representing a group of objects as a single entity.
LinkedList is the implemetation class for List interface Introduced in 1.2 version
Underlying data Structure is DoubleLinkedList Allows duplicates
Insertion order is preserved
Allows heterogeneous objects
null insertion is possible
LinkedList class implements Seriallizable and Cloneable interface but not RandomAccess interface
Best choice if frequent operation is insertion or deletion an objects in middle but worst choice if frequent operation is retrieval.

Q344. Explain about Vector class?
Vector is a legacy collection class which can be used to represent a group of objects.
Introduced in 1.0 version. it is legacy class
The underlying data structure is resizable or growable array. Insertion order is preserved
Duplicates are allowed
Heterogeneous objects are allowed
It is a implemented class for List interface null insertion is possible
Vector class implements RandomAccess ,Serializable,Cloneable interfaces
Best Choice if frequent operation is retrieval and worst choice if frequent operation is insertion or deletion in the middle.
All methods present in Vector class are synchronized hence Vector class object is thread safe.

Q345. How we can get synchronized version of ArrayList?
Collections class contains synchronizedList() method for this
Public static List synchronizedList(List l)
EX
ArrayList l= new ArrayList();
List l2=Collections.synchronizedList(l);
Similarly we can get synchronized versions of Set and Map objects by the following methods. Public static List synchronizedSet(Set s)
Public static List synchronizedMap(Map m)

Q346. What is difference between size and capacity of a Collection Object?
size means number of objects present where as capacity means no of objects it can accommodate.

Q347. What are legacy classes and interfaces present in Collections framework ?
Enumeration ---Interface
Dictonary ------Abstract class
Hashtable -----Concrete class
Properties -----Concrete class
Vector -----Concrete class Stack -----Concrete class

Q348. What are limitations of Enumeration?
While iterating the elements we are not allowed to perform removal operation It is applicable only for legacy classes and it is not a universal cursor.It can retrieve the elements only in forward direction.

Q349. What is difference between enum and Enumeration?
An enum can be used to define a group of named constants .It has introduced in 1.5 version Ex
Class Beer{
KO,KF,RC,FO
}
Enumeration is cursor to retrieve Objects one by one from Collection objects.

Q350. What is difference between Iterator and ListIterator?
o ListIterator is the child interface of the Iterator
o Iterator is the single direction cursor where as ListIterator is bidirectional cursor. o While iterating the elements by Iterator we can perform only read and remove
operations. But by using ListIterator we can perform read,removal, replace and
addition of new objects also.
o Iterator is applicable for every Collecton implemented class object but
ListIterator is applicable only for List implemented class objects.
o Iterator can be get by using iterator() of Collection interface where as ListIterator
can be get by using listIterator() method of List interface
o both are introduced in 1.2 version

JAVA interview questions 34

2012-05-01T05:22:00.000-07:00

Q331. What is Collection framework?
It defines set of classes and inter faces which can be used for representing a group of objects as single entity

Q332. What is difference between Collections and Collection?
Collection is an interface which can be used for representing a group of individual objects as single entity and it acts as root interface of collection frame work.
Collections is an utility class to define several utility methods for Collection implemented class objects.

Q333. Explain about Collection interface?
* This interface can be used to represent a group of objects as a single entity. * It acts as root interface for entire collection framework.
* It defines the most commonly used methods which can be applicable for any collection implemented class object
Q339. Explain about List interface?
List interface is a child interface of Collection interface. This can be used to represent group of individual objects in as a single entity where
* Duplicates are allowed
* Insertion order is preserved

Q334. Explain about Set interface?
Set is a child interface of Collection interface. it can be used to represent a group of individual objects as a single entity where
* Duplicate objects are not allowed.
* Insertion order is not preserved

Q335. Explain about SortedSet interface?
it is child interface of Set interface. it can be used to represent a group of individual objects in to a single entity where
All the objects are arranged in some sorting order (Can be natural sorting order or customizede).
Duplicates are not allowed.

Q336. Explain about NavigableSet ?
It is child interface of SortedSet and provides several utility methods for navigation purposes
It doesn’t allows duplicates
Insertion order is preserved
It is introduced in 1.6 version

Q337. Explain about Queue interface?
If we want to represent a group of individual objects prior to processing, then we should go for Queue interface. It is child interface of Collection interface.
It has introduced in 1.5 version.

Q338. Explain about Map interface?
Remember it is not a child Interface of Collection Interface and hence Map and Collection Interfaces doesn’t have any relationship.
It can be used for representing a group of Objects as key, value pairs. Both keys and values should be objects
Keys can t be duplicated but values can be duplicated. it has introduced in 1.2 version

Q339. Explain about SortedMap ?
If we want to represent a group of objects as key value pairs where all the entries are arranged according some sorting order of keys then we should go for SortedMap. It is child interface of Map.
It has introduced in 1.2 version

Q340. Explain about NavigableMap?
It is child interface of SortedMap and defines several method for navigation purpose It is introduced in 1.6 version

JAVA interview questions 33

2012-05-01T05:19:00.000-07:00

Q321.Explain about Thread group?
Ans. Every Java thread is a member of a thread group. Thread groups provide a mechanism for
collecting multiple threads into a single object and manipulating those threads all at once, rather
than individually. For example, you can start or suspend all the threads within a group with a
single method call. Java thread groups are implemented by the ThreadGroup api class in the java.lang package.

Q322.What is the Thread Local?
Ans. It's a way for each thread in multi-threaded code to keep its own copy of an instance
variable. Generally, instance variable are shared between all threads that use an object; ThreadLocal is a way for each thread to keep its own copy of such a variable. The purpose might be that each thread keeps different data in that variable, or that the developer wants to avoid the overhead of synchronizing access to it.

Q323. What is inner class and when we should go for inner classes?
Some times we can declare a class inside another class such type of classes are called inner classes
Example
Class Car{
//more code here
Class Engine{
//more code here }
}
Without existing Car object there is no chance of existing Engine object, hence Engine class has declared inside Car class.

Q324.How many types of inner classes are present?
There are four types of inner classes are present
o Normal or regular inner class o Method local inner class o Anonymous inner class o Static nested class

Q325.What is method local inner class?
Sometimes we can declare a class inside a method such type of classes are called method local
inner classes
The main purpose of method local inner classes is to define method specific functionality The scope of method local inner classes is the scope of the method where it is declared. This is the mostly rarely used type of inner classes.
Example
class Test{
public void m1(){
class Inner {
public void sum(int I,int j){
System.out.println(i+J);
}//sum
}//inner
Inner i=new Inner();
i.sum(10,20);
//more code here
I.sum(100,303);
//more code here
i.sum(102,84);
}//m1()
Public static void main(){
New Test().m1();
}
}

Q326.What is anonymous inner class?
Some times we can declare a inner class without name such type of inner classes are called
Anonymous inner classes
Anonymous inner classes can be divided into 3 categories
§ Anonymous inner class that extends a class
§ Anonymous inner class that implements an interface
§ Anonymous inner class that defines inside a method argument
ANONYMOUS INNER CLASS THAT EXTENDS A CLASS Example
Class popcorn{
Public void taste(){
System.out.println(“it is salty”);
}
//more code here
}
Class Test{
Public static void main(String[] args)
{
Popcorn p=new Popcorn()
{ // here we are creating child class for popcorn
Public void taste(){
System.out.println(“it is sweet”);
}
};//here semicolon indicates we r creating child class object with parent
// class reference here child class dosent contain name
p.taste()// it is sweet
Popcorn p=new Popcorn();
p1.taste() //it is salty }
}

ANONYMOUS INNER CLASS THAT IMPLEMENTS AN INTERFACE example
class Test{
Public static void main(String[] args){
Runnable r=new Runnable(){
Public void run(){
for(int i=0;i<10;i++){
System.out.printin(“child thread”);
}
}
};
Thread t=new Thread(r);
t.start();
for(int i=0;i<10;i++){
System.out.printin(“main thread”); }
}
}
Don’t become fool that here we are creating object of interface Runnable.Here we are actually
creating an object of class that is implemented Runnable interface.

Q327.What is static nested calss?why the term nested instead of inner in static nested class?
Some times we can declare inner class with static modifier such type of inner class are called static
nested classes.the term nested instead of static because without existing outer class object inner
class object can exist.
Example
Class outer{
Static class Nested{
Public static void main(String[] args){
System.out.println(“nested class main()”); }
}
Public static void main(String[] args){
System.out.println(“outer class main()”); }
}
Java Outer
O/P
Outer class main() Java Outer$Nested
O/P
Nested class main()

Q328. Inside inner class is it possible to declare main()?
No it is not possible to declare main () inside inner class but in static nested class it is possible for
Example refer above code

Q329. What are limitations of object Arrays?
The main limitations of Object arrays are
* These are fixed in size ie once we created an array object there is no chance of increasing or decreasing size based on our requirement. Hence If we don’t know size in advance , arrays are not recommended to use
* Arrays can hold only homogeneous elements.
* There is no underlying data structure for arrays and hence no readymade method support for arrays. Hence for every requirement programmer has to code explicitly
To over come these problems collections are recommended to use.

Q330. What is Collection API ?
It defines set of classes and interfaces which can be used for representing a group of objects as single entity

JAVA interview questions 32

2012-05-01T05:15:00.000-07:00

Q311. What is race condition?
Ans. Multiple Threads are accessing simultaneously and causing data inconsistency problem is called race condition, we can resolve this by using synchronized keyword.

Q312. What is Daemon Thread? And give an example?
Ans. The Threads which are running in the background are called Daemon Thread.
Example: Garbage collector.

Q313. What is the purpose of a Daemon Thread?
Ans. The main purpose of Daemon Threads is to provide support for non-daemon Threads.

Q314. How we can check Daemon nature of a Thread?
Ans. We can check Daemon nature of a Thread by using isDaemon() method.

Q315. Is it possible to change a Daemon nature of a Thread?
Ans. Yes, we can change Daemon nature of a Thread by using setDaemon() method.

Q316. Is main thread is Daemon or non-daemon?
Ans. By default main thread is always non-daemon nature.

Q317. Once we created a new thread is it daemon or non-daemon.
Ans. Once we created a new Thread, The Daemon nature will be inheriting from parent to child. If the parent is Daemon the child is also Daemon and if the parent is non-daemon then child is also non-daemon.

Q318. After starting a thread is it possible to change Daemon nature?
Ans. We can change the Daemon nature before starting the Thread only. Once Thread started we are not allow to change Daemon nature otherwise we will get RuntimeException sying IllegalThreadStateException.

Q319. When the Daemon thread will be terminated?
Ans. Once last non-daemon Thread terminates automatically every Daemon Thread will be terminated.

Q320. What is green Thread?
Ans. A green thread refers to a mode of operation for the Java Virtual Machine (JVM) in which all code is executed in a single operating system thread. If the Java program has any concurrent
threads, the JVM manages multi-threading internally rather than using other operating system threads.
There is a significant processing overhead for the JVM to keep track of thread states and swap between them, so green thread mode has been deprecated and removed from more recent Java implementations.

JAVA interview questions 31

2012-05-01T05:13:00.000-07:00

Q301.If a waiting thread got notification then it will entered into which state?
Ans. It will entered into another waiting state to get lock.

Q302.In which method threads can release the lock?
Ans. Once a Thread calls wait() method it immediately releases the lock of that object and then entered into waiting state similarly after calling notify() method Thread releases the lock but may not immediately. Except these three methods( wait(), notify(), notifyAll() ) method Thread neverreleases the lock anywhere else.

Q303. Explain wait(), notify(), notifyAll() method uses.
Ans. Two Threads will communicate with each other by using wait(), notify() or notifyAll() methods.
These methods are defined in Object class but not in Thread because Threads are calling this method.

Q304. What is the difference between notify() and notifyAll()?
Ans. To give notification to the single waiting Thread. We use notify() method and to give notification to all waiting thread we use notifyAll() method.

Q305. Once a Thread got the notification then which waiting thread will get chance?
Ans. It is depends on the Thread Scheduler.

Q306. How a thread can interrupt another thread?
Ans. A Thread can interrupt another Thread by using interrupt() method.

Q307. Which keyword causes DeadLock situation?
Ans. Synchronized keyword is the thing to causes of DeadLock. If we are not using properly synchronized keyword the program will entered into DeadLock situation.

Q308. How we can stop a thread explacitly?
Ans. Thread class defines stop() method by using this method we can stop a Thread. But it is deprecated. And hence not recommended to use.

Q309. Explain about suspend() and resume() method?
Ans. A Thread can suspend another Thread by using suspend() method.
A Thread can resume a suspended Thread by using resume() method.

Q310.What is Starvation()? And Explain the difference between Deadlock and Starvation?
Ans. A long waiting Thread is said to be in starvation (because of least priority) but after certain time defiantly it will get the chance for execution. But in the case of Deadlock two Threads will wait for each other forever. It will never get the chance for execution.

JAVA interview questions 30

2012-04-30T07:13:00.000-07:00

Q291. What is object lock? Explain when it is required?
Ans. Every object in java has a unique lock whenever we are using synchronization concept then only lock concept will coming to the picture.
If a Thread wants to execute a synchronized method first it has to get the lock of the object. Once a Thread got the lock then it is allow to execute any synchronized method on that object. After completing synchronized method execution Thread releases the lock automatically.While a
Thread executing synchronized method on the given object the remaining Threads are not allow to execute any synchronized method on that object simultaneously. But remaining Threads are allow to execute any non-synchronized method simultaneously. (Lock concept is implemented based on object but not based on method.)

Q292.What is the class level lock? Explain its purpose.
Ans. Every class in java has a unique lock if a Thread wants to execute static synchronized
method that Thread has to get class level lock once a Thread got class level lock then only it is allow to execute static synchronized method.
While a Thread executing any static synchronized method then remaining Threads are not allow to execute any static synchronized method of the same class simultaneously. But the remaining Threads are allow to execute the following method simultaneously:
1. Any static non-synchronized method.
2. Synchronized instance methods
3. Non-synchronized instance method.
There is no relationship between object lock and class level lock, both are independent.

Q293. While a thread executing any synchronized method on the given object is it possible toexecute remaining synchronized method of the same object simultaneously by any other thread?
Ans. No, it is no possible.

Q294. What is the difference between synchronized method and static synchronized method?
Ans. If a Thread wants to execute a synchronized method first it has to get the lock of the
object. Once a Thread got the lock then it is allow to execute any synchronized method on that
object.If a Thread wants to execute static synchronized method that Thread has to get class
level lock once a Thread got class level lock then only it is allow to execute static synchronized method.

Q295. What is the advantage of synchronized block over synchronized method?
Ans. If very few lines of the code required synchronization then declaring entire method as the synchronized is not recommended. We have to declare those few lines of the code inside
synchronized block. This approach reduces waiting time of the Thread and improves performance of the system.

Q296. What is synchronized statement?
Ans. The Statement which is inside the synchronized area (synchronized method or synchronized block) is called synchronized statement.

Q297. How we can declare synchronized block to get class level lock?
Ans. To get the class level lock we can declare synchronized block as follows:
synchronized(Display.class)
{
}

Q298. How two thread will communicate with each other?
Ans. Two Threads will communicate with each other by using wait(), notify(), notifyAll() methods.

Q299.wait(), notify(), notifyAll() method can available in which class?
Ans. These methods are defined in Object class.

Q300.Why wait(), notify(), notifyAll() method defines in object class instead of Thread class?
Ans. These methods are defined in Object class but not in Thread because Threads are calling this method on the shared object.

JAVA interview questions 29

2012-04-30T07:08:00.000-07:00

Q281. If we are trying to set priority of a Thread as 100 what will happen?
Ans. If we are trying to set priority of a Thread as 100 then we will not get any compile time error but at the runtime we will get Runtime exception IllegalArgumentException. Because the valid range of the Thread priority is (1-10) only.

Q282. If two threads having same priority then which thread will get chance first for execution?
Ans. If two threads having same priority then which thread will get the chance first for execution decided by Thread Scheduler. It is the part of JVM and its behavior is vendor dependent and we can’t expect exact output.

Q283. If two threads having different priority then which thread will get chance first for execution?
Ans. If two threads having different priority then the Thread which is having highest priority will get chance first for execution.

Q284 .How we can prevent a thread from execution?
Ans. We can prevent a Thread from executin by using the following methods:
1. Yield()
2. Join()
3. Sleep()

Q285. What is yield() method? Explain its purpose?
Ans. yield() method causes the current executing thread to pause execution and give the chance for waiting thread are same priority. If there is no waiting thread or all the remaining waiting thread have low priority then the same thread will get chance once again for execution. The
Thread which is yielded when it will get chance once again for execution depends upon mercy of Thread scheduler.Public static native void yield();

Q286.What is purpose of join() method?
Ans. If a Thread wants to wait until some other Thread completion then we should go for join() method.
Example: if a Thread t1 execute t2.join() ; then t1 will entered into waiting state until t2 Thread completion.

Q287. Is join() method is overloaded?
Ans. Yes join() method is overloaded method.
Public final void join() throws InterruptedException
By using this method thread will wait up to another thread completion .
Public final void join(long ms) throws InterruptedException
By using this method thread will wail upto sometime what we are passing as a argument in millisecond
Public final void join(long ms, int ns)throws InterruptedException
By using this method thread will wait up to sometime what we are passing as a argument in millisecond and nanosecond.

Q288. What is the purpose of sleep() method?
Ans. If a Thread don’t want to perform any operation for a particular amount of time then we should go for sleep() method.Whenever we are using sleep() method compulsory we should
handle InterruptedException either by using try-catch or by using throws keyword otherwise we will get compile time error.

Q289. What is synchronized keyword? Explain its advantages and disadvantages.
Ans. Synchronized keyword is applicable for method and blocks only. We can’t use for
variables and classes.
If a method declared as a synchronized then at a time only one Thread is allow to
execute that method on the given object.
The main advantages of synchronized keyword are, we can prevent data inconsistency problems and we can provide Threadsafty.
But the main limitation of synchronized keyword is it increases waiting time of
Threads and effect performance of the system. Hence if there is no specific requirement it is not recommended to use synchronized keyword.

Q290.Where we can use synchronized keyword?
Ans. Synchronization concept is applicable whenever multiple Threads are operating on the same object simultaneously. But whenever multiple Threads are operating on different objects then there is no impact of synchronization.

JAVA interview questions 28

2012-04-30T07:06:00.000-07:00

Q271. Explain life cycle of a Thread?
Ans. Once we create a Thread object then the Thread is said to be in New/Born state once we call t.start() method now the Thread will be entered into ready/Runnable state that is Thread is ready to execute. If Thread Scheduler allocates CPU now the Thread will entered into the Running state and start execution of run() method. After completing run() method the Thread entered into Dead State.

Q272. What is the importance of Thread class start() method?
Ans. Start() method present in Thread class performing all low level joining formalities for the newly created thread like registering thread with Thread Scheduler etc and then start() method
invoking run() method.As the start() method is doing all low level mandatory activities,
Programmer has to concentrate only on run() method to define the job. Hence, start() method is a big assistant to the programmer.Without executing Thread class start() method there is no chance of starting a new Thread.

Q273. After starting a Thread if we trying to restart the same thread once again what will happen?
Ans. After starting a Thread restarting of the same Thread once again is not allowed violation leads to Runtime Exception saying IllegalThreadStateException.

Q274. Explain Thread class constructors?
Ans. There are eight constructors are available in Thread class:
1. Thread t=new Thread();
2. Thread t=new Thread(Runnable r);
3. Thread t=new Thread(String name);
4.Thread t=new Thread(Runnable r, String name);
5.Thread t=new Thread(ThreadGroup g, String name);
6.Thread t=new Thread(ThreadGroup g, Runnable r);
7.Thread t=new Thread(ThreadGroup g, Runnable r, String name);
8.Thread t=new Thread(ThreadGroup g, Runnable r, String name, long stacksize);

Q275. How to get and set name of a Thread?
Ans. For every Thread in java there is a name. To set and get the name of a Thread we can use the following methods. All methods are final.
1.Public final void setName(String name); - To set the name of a Thread
2.Public final String getName(); - To get the name of a Thread.

Q276. What is the range of Thread priority in java?
Ans. The valid range of a Thread priority is 1-10. (1 is least priority and 10 is highest priority)

Q277. Who uses Thread priority?
Ans. Thread Scheduler uses priorities while allocating CPU. The Thread which is having highest priority will get chance first for execution.

Q278. What is the default priority of the Thread?
Ans. The default priority only for the main thread is 5 but for all remaining threads default
priority will be inheriting from parent to child. Whatever priority parent thread has the same will be inherited to the child thread.

Q279. Once we created a new Thread what about its priority?
Ans. Whatever priority parent thread has the same will be inherited to the new child thread.

Q280. How to get and set priority of a Thread?
Ans. To get and set priority of a Thread, Thread class defines the following two methods:;
1. Public final int
getPriority();
2. Public final void setPriority(int priority);

JAVA interview questions 27

2012-04-30T07:04:00.000-07:00

Q261. What is Multithreading and explain its application areas?
Ans. Executing several thread simultaneously where each thread is a separate independent part of the same program is called multithreading. Java language provides inbuilt support for
multithreading by defining a reach library, classes and interfaces like Thread, ThreadGroup,
Runnable etc. The main important application area of multithreading are video games implementation, animation development, multimedia graphics etc.

Q262.What is advantage of Multithreading?
Ans. The main advantage of multithreading is reduces response time and improves performance of the system.

Q263. When compared with C++ what is the advantage in java with respect to Multithreading?
Ans.Java language provides inbuilt support for multithreading by defining a reach library, classes and interfaces like Thread, ThreadGroup, Runnable etc. But in c++ there is no inbuilt support for multithreading.

Q264. In how many ways we can define a Thread? Among extending Thread and implementing Runnable which is recommended?
Ans. We can define a Thread in the following two ways:
1. by extending Thread class or
2. by implementing Runnable interface.

Among the two ways of defining a thread implementing Runnable mechanism is always
recommended. In the first approach as our Thread class already extending Thread there is no chance of extending any other. Hence, we missing the key benefit of oops(inheritance properties).

Q265. What is the difference between t.start() and t.run() method?
Ans. In the case of t.start() method, a new thread will be created which is responsible for the
execution of run() method.
But in the case of t.run() method no new thread will be created main thread executes
run() method just like a normal method call.

Q266. Explain about Thread Scheduler?
Ans. If multiple threads are waiting for getting the chance for executing then which thread will get chance first decided by Thread Scheduler. It is the part of JVM and its behavior is vendor dependent and we can’t expect exact output.Whenever the situation comes to multithreading the guarantee behavior is very- very low.

Q267. If we are not overriding run() method what will happened?
Ans.If we are not overriding run() method then Thread class run() method will executed which has empty implementation and hence we will not get any output.

Q268.Is overloading of run() method is possible?
Ans.Yes, we can overload run() method but Thread class start() method always invokes no-
argument run() method only. The other run() method we have to call explicitly then only will be executed.

Q269.Is it possible to override start() method?
Ans. Yes it is possible. But not recommended.

Q270.If we are overriding start() method then what will happen?
Ans. It we are overriding start() method then our own start() method will be executed just like a normal method call. In this case no new Thread will be created.

JAVA interview questions 26

2012-04-30T06:59:00.001-07:00

Q251. Which class act as root for entire java Exception hierarchy?
Ans. Throwable class act as root for entire java Exception hierarchy.

Q252. What is the difference between Error and Exception?
Ans. Throwable class contain two child classes.
Exception:- These are mostly caused by our program and are recoverable.
Error:- These are not caused by our program, mostly caused by lake of system resources. These are non recoverable.

Q253. What is difference between checked exception and unchecked exception?
Ans. The exceptions which are checked by the compiler for smooth execution of the program at Runtime is called checked exception. Example: IOException, InterruptedException.The
exceptions which are not checked by the compiler are called unchecked exception. Example: ArithmeticException,RuntimeException.

Q254.What is difference between partially checked and fully checked Exception?
Ans. A checked exception is said to be fully checked if and only if all the child classes also checked otherwise it is called partially checked exception.
Example:
IOException:- fully checked exception
Exception:- partially checked exception
Throwable:- partially checked exception
RuntimeException:- unchecked exception

Q255. What is a customized Exception?
Ans. Sometimes based on our programming requirement we have to create our own exception such type of exception are called customize Exception.
Example:
TooYoungException
TooOldException
InsufficientFundException

Q256. Explain the process of creating the customized Exception.
Ans. Creating customized Exception:
Class TooYoungException extends RuntimeException{ TooYoungExcetpion(String desc){
Super(desc);
}
}
Class TooOldException extends RuntimeException {
TooOldException(String desc){
super(desc);
}
}
Class custExcepiton{
Public static void main(String[] args){ int age=Integer.parseInt(args[0]);
if(age>60)
{
Throw new TooYoungException(“Please wait some more time, definitely you will get best match”);
}
else if(age<18) {
Throw new TooOldException(“Your age is already crossed of marriage, no chance to getting marriage”);
}
else {
System.out.println(“Congratulation! You will get match details soon by your
email”);
}
}

Q257. Explain control flow in try, catch, finally.
Ans. try{
Statement1;
Statement2;
Statement3;
}
catch(X e){
Statement4; }
Finally{
Statement5; }
Statement6;
Case1:
If there is no Exception then output is
Statement1
Statement2
Statement3
Statement5
Statement6
Normal termination
Case2:
If an exception raised at statement2 and corresponding catch block has matched then output is Statement1
Statement4
Statement5
Statement5
Normal termination
Case3:
An exception raised at statement2 and corresponding catch has not matched then output is Statement1
Statement5
Abnormal termination
Case4:
An exception occurs at statement4 it always Abnormal termination but before that finally block will be executed and output is
Statement1
Statement2
Statement5
Abnormal termination
Case5:
If an exception raised at statement5 or statement6, it is always abnormal termination.

Q258. Can you give the most common occurred exception in your previous project.
Ans. NullPointerException, ArrayIndexOutofBoundException, StackOverFlowError,
ClassCastException, NoClassDefFoundError, ExceptionInitilizerError,
IllegalArgumentException, NumberFormatException, IllegalStateException, AssertionError.

Q259. What is Multitasking?
Ans. Executing several task simultaneously is called multitasking.

Q260. What is the difference between process-based and Thread-based Multitasking?
Ans.Process-based multitasking:- Executing several task simultaneously where each task is a
separate independent process such type of multitasking is called process based Multitasking.
Example:-While typing a program in the editor we can listen MP3 audio songs. At the same time we download a file from the net. all these task are executing simultaneously and each task is
a separate independent program. hence it is process based multitasking. It is best suitable at operating system level. Thread-based multitasking:-Executing several task simultaneously where each task is a separate independent part of the same program is called Thread-based multitasking. and every independent part is called a thread. This type of multitasking is best suitable at programmatic level.

JAVA interview questions 25

2012-04-28T08:44:00.000-07:00

Q241. What is the purpose of throw?
Ans. Sometimes we can create Exception object explicitly and we can handover that exception object to the JVM explicitly by throw keyword.
The purpose of throw keyword is to handover our created exception object explicitly to the
JVM.
Example1:
class Test{
public static void main(String[] args){
System.out.println(10/0);
}
}
In this case ArithmeticException object created implicitly and handover to the JVM automatically by the main method.
Example2:
class Test{
Public static void main(String[] args){
Throw new ArithmeticException(“/by Zero”); }
}
In this case creation of an exception object and handover to the JVM explicitly by the programmer.

Q242. Is it possible to throw an Error?
Ans. Yes, It is possible to throw any Throwable type including Error.

Q243. Is it possible to throw any java object?
Ans. No, we can use throw keyword only for throwable objects otherwise we will get compile time error saying incompatible type.
* Core Java
* Servlets & JSP
* Struts
* EJB
* J2ME

Q244. After throw is it allow to take any statement directly?
Ans. After throw statement we are not allow to place any statement directly violation leads to compile time error saying Unreachable Statement.

Q245. What is the purpose of throws?
Ans. The main purpose of throws keyword is to delegate the responsibilities of exception handling to the caller. It requires in the case of checked exception.

Q246. What is the difference between throw and throws?
Ans. Sometimes we can create Exception object explicitly and we can handover that exception object to the JVM explicitly by throw keyword.The main purpose of throw keyword is to
handover our created exception object explicitly to the JVM. The main purpose of throws
keyword is to delegate the responsibilities of exception handling to the caller. It requires in the case of checked exception.

Q47. What is the difference between throw and thrown?
Ans. There is no terminology of thrown in java.

Q248. Is it possible to use throws keyword for any java class?
Ans. No, we can use throws keyword only for Throwable classes. Otherwise we will get compile time error saying Incompatible types.

Q249. If we are taking catch block for an exception but there is no chance of rising that exception in try then what will happen?
Ans. If there is no chance of raising an exception in try then we are not allow to write catch
block for that exception violation leads to compile time error. But this rule is applicable only for fully checked exception.

Q250. Explain Exception Handling keyword?
Ans. Exception Handling keyword: Try :- To maintain Risky code.
Catch:- To maintain Exception Handling code. Finally:- To maintain the clean up code.
Throw:- To handover our created exception object to the JVM explicitly.
Throws:- To delegate the responsibilities of Exception Handling to the caller.

JAVA interview questions 24

2012-04-28T08:40:00.000-07:00

Q231.Is it possible to take try, catch inside catch block?
Ans. Yes, It is possible to take try, catch inside catch block.

Q232. Is it possible to take try without catch?
Ans. Yes, it is possible to take try without catch but compulsory finally block should be available.

Q233. What is the purpose of finally block?
Ans. The main purpose of finally block is, to maintain the cleanup code. This block will execute always.

Q234. Is finally block will be execute always?
Ans. Yes finally block will be executed always irrespective of whether exception raised or not raised whether exceptions are handled or not handle. There is one situation where the finally block won’t be executed if the JVM is going to be shutdown.

Q235. In which situation finally block will not executed?
Ans. There is one situation where the finally block won’t be executed if we are using
system.exit(0) explicitly then JVM itself will be shutdown and there is no chance of executing finally block.

Q236. If return statement present inside try is finally block will be executed?
Ans. Yes, if return statement present inside try, then also finally block will be executed. finally block will dominate return statement also.

Q237. What is the difference between final, finally and finalize()?
Ans. final:- final is a modifier applicable for variables, methods and classes. final variable
means constant and reassignment is not possible. final method means implementation is final in the child classes we can’t override. final class means it won’t participate in inheritance and child class creation is not possible.
finally:- It is a block associated with try catch to maintain cleanup code. Finally block will be executed always irrespective of whether exception is raised or not raised or whether the exception is handle or not handle.
finalize():- It is a method, Garbage collector always calls this method just before destroying any object to perform cleanup activities.

Q238. Is it possible to write any statement between try-catch and finally?
Ans. No, it is not possible to write any statement between try catch and finally. If we will try to write any statement between them then we will get compile time error.

Q239. Is it possible to take two finally blocks for the same try?
Ans. No, it is not possible to take two finally blocks for the same try. If we try to take then we will get compile time error.

Q240. Is syntax try-finally-catch is valid ?
Ans. No, this syntax is not valid. It should be like try-catch-finally then only code will compile.