Java EnterPrise Edition

J2EE Interview Questions And Answers (part 2)

2009-10-19T02:59:00.000-07:00

21)What's the difference between the == operator and the equals() method? What test does

Object.equals() use, and why?

The == operator would be used, in an object sense, to see if the two objects were

actually the same object. This operator looks at the actually memory address to see if it

actually the same object. The equals() method is used to compare the values of the

object respectively. This is used in a higher level to see if the object values are equal.

Of course the the equals() method would be overloaded in a meaningful way for

whatever object that you were working with.

22)why do you create interfaces, and when MUST you use one.

You would create interfaces when you have two or more functionalities talking to each other. Doing it this

way help you in creating a protocol between the parties involved.

23)What is the difference between instanceof and isInstance?

instanceof is used to check to see if an object can be cast into a specified type without throwing a cast class

exception.

isInstance()--Determines if the specified Object is assignment-compatible with the object represented by this Class. This method is the dynamic equivalent of the Java language instanceof operator. The method returns true if the specified Object argument is non-null and can be cast to the reference type represented by this Class object without raising a

ClassCastException. It returns false otherwise.

24)How many methods do u implement if implement the Serializable Interface?

The Serializable interface is just a "marker" interface, with no methods of its own to implement.

Are there any other 'marker' interfaces?

java.rmi.Remote

java.util.EventListener

25)Name four methods every Java class will have.

public String toString();

public Object clone();

public boolean equals();

public int hashCode();

26)What does the "abstract" keyword mean in front of a method? A class?

Abstract keyword declares either a method or a class. If a method has a abstract keyword in front of it,it is called abstract method.Abstract method hs no body.It has only arguments and return type.

Abstract methods act as placeholder methods that are implemented in the subclasses.Abstract classes can't be instantiated.If a class is declared as abstract,no objects of that class can be created.If a class contains any abstract method it must be declared as abstract.

27)Does Java have destructors?

No garbage collector does the job working in the background

28)Are constructors inherited? Can a subclass call the parent's class constructor? When?

You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses. One of the main reasons is because you probably don't want to overide the superclasses constructor, which would be possible if they were inherited. By giving the developer the ability to override a superclasses constructor you would erode the encapsulation abilities of the language.

29)What does the "final" keyword mean in front of a variable? A method? A class?

FINAL for a variable : value is constant

FINAL for a method : cannot be overridden

FINAL for a class : cannot be derived

30)Access specifiers: "public", "protected", "private", nothing?

Public – any other class from any package can instantiate and execute the classes and methods

Protected – only subclasses and classes inside of the package can access the classes and methods

Private – the original class is the only class allowed to executed the methods.

Free Java E-Books Download Sites

2009-10-16T22:54:00.000-07:00

Some of the good sites where you can download java books for free.

www.techbooksforfree.com----This site provides free books on Java,Linux,Perl,Python,Networking,Database,C,C++ and Security.

http://jaganguys.com/----This is one of my favourite sites which offers books starting from programming languages to Aptitude books.one location where you can find books for every stream related to computers.If you are looking for books written by great authors then this is the right place.

www.java201.com/----This site provides resources for server-side developers and also some good java E-books.

http://freecomputerbooks.com/---It provides all E-bboks related to programming languages and you can search books ranging from web designing,data bases,Linux/Unix,.NET,etc.

www.freebookcentre.net/----This site is very good and has E-books ranging from Computer Science,Computer Languages,Java / Advanced Java,Unix/Linux,Web Technology,Database Systems,Networking,Microsoft Technology,Special Topics,Miscellaneous,Oreilly Books,Cisco Certification,Medical books.

www.ebookslab.info/-----It provides a wide range of E-books

www.onlinecomputerbooks.com/--------it doesn't even miss out a single book ranging from Programming languages to Web site Designing.

www.ebooks-space.com/-------Computer IT,Programming Language,Software Develpoment,Tutorial,Database.

J2EE Interview Questions And Answers (part 1)

2009-10-16T01:19:00.001-07:00

The Following JSP interview questions, servlets interview questions, Java architect interview questions can help you get through an interview (1 to 20)

1)What is a singleton class?How do you write it? Illustrate with an example?

A class which must create only one object (ie. One instance) irrespective of any number of object created based on that class.

Steps to develop single ton class:-

(i)Create a Private construtor, so that outside class can not access this constructor. And declare a private static reference of same class

(ii)Write a public Factory method which creates an object. Assign this object to private static Reference and return the object

Sample Code:-

class SingleTon

{

private static SingleTon st=null;

private SingleTon()

{

System.out.println(“\nIn constructor”);

}

public static SingleTon stfactory()

{

if(st==null)

st=new SingleTon();

return st;

}

2) What is the difference between using HttpSession & a Stateful Session bean? Why can't HttpSession be used instead of of Session bean?

HttpSession is used to maintain the state of a client in webservers which are based on Http protocol. Where as Stateful Session bean is a type of bean which can also maintain the state of the client in Application servers based on RMI-IIOP

3)What is Temporary Servlet?

When we send a request to access a JSP, servlet container internally creates a 'servlet' & executes it. This servlet is called as 'Temporary servlet'. In general this servlet will be deleted immediately. to create & execute a servlet base on a JSP we can used following command.

Java weblogic.jspc—keepgenerated *.jsp

4) Generally Servlets are used for complete HTML generation. If you want to generate partial HTML's that include some static text (this should not be hard coded in servlets) as well as some dynamic text, what method do you use?

Using 'RequestDispather.include(“xx.html”) in the servlet code we can mix the partial static HTDirectoryML page.

Ex:- RequestDispatcher rd=ServletContext.getRequestDispatcher(“xx.html”);

rd.include(request,response);

5)Difference between jsp:forward and jsp:include tags?

jsp:forward action tag redirect the servlet Request and Servlet Response to another resource specified in the tag. The path of the resource is 'relative path'. The output generated by current JSP will be discarded.

jsp:include action tag process the resource as part of the current jsp. It include the o/p generated by resource, which is specified in the Tag to the current JSP

(*) In both the cases single Request proceses multiple resources

6)Purpose of jsp:plugin tag

It is used to generate client browser specified HTML tags which results in download of the java plugin software. And the execution of the applet or java Bean component that is specified in the tag.

7)Which method is called first each time a Servlet is invoked?

When the servlet obj is not created init() method will be called. It servlet object already exists service() method will be called.

8)Why DB connections are not written directly in JSP's?

The main purpose of JSP is to seperate the business logic & presentation logic. DB connections deal with pure java code. If write this kind of code in JSP, servlet container converts the JSP to servlet using JSP compiler which is the time consuming process so this is better to write code wich deals with DB connections, Authentication and Authorization etc. in the java bean and use the tag to perform the action.

9)What is key diffrence between using an jsp:forward tag and HttpServletResponse.sendRedirect()?

Ans: The jsp:forward action tag allows the request to be forwarded to another resource (servlet/jsp/HTML) which are available in the same web-application (context).

Where as in the case of Response.sendRedirect() the request to be forwarded/redirected to another resource in the same web-application or some other web-application in the same server, or to a resource on some other web-server. The key difference is by using jsp:forward tag

single request from a browser can process multiple resources. Where as by using SendRedirect() multiple requests take place in order to process multiple resources.

10)Why beans are used in J2EE architecture instead of writing all the code in jsp's?

In order to seperate the business logic and presentation logic beans are used. We write the business logic in the Beans. Where there is a change in business process we have to modify only the bean code not jsp code and viceversa.

11)How can a servlet can call JSP error page?

By simply including an error-page tag in “web.xml” file

error-page

exception-type javax.servlet.ServletException /exception-type

location /error.jsp /location

the placement of the error file i.e /errorjsp.jsp within the location tags and then the end tag of error-page

By using Response.sendRedirect(“error.jsp”); or by using RequestDispatcher.forward(“error.jsp”); we can call jsp error page in servlet.

12)Explain MVC (Model-View-Controller) architecture?

MVC:- In model view controller design pattern, the software has split into 3 pieces.

MODEL-> Responsible for Managing Data-> Ex. Java Beans

VIEW-> Responsible for generating the views->Ex. Jsp's

CONTROLLER-> Responsible for user interactions & co-ordinate with MODEL &VIEW

13)what are JSP implicit Objects:-

out: used to send the content to the browser

ex: out.println(“xx”)

Response: Represent HttpServlet Reques

Response: Represent HttpServletResponse

Page Context: used to access the objects like session, servlet context, Request, Response etc...

Session: Points to HttpSession objects

Application: Points to servlet context objects

Page: Points to current servlet objects

Exception: Points to Exception

14)JSP Action Tags, Directive Tags & Scripting Tags?

Action Tag: These tags effect the runtime behaviour of the jsp page and the response set back to client tags are :

jsp: usebean tag : instantiates a new jsp bean class

jsp: setProperty tag : setting the properties at runtime

jsp:param tag : used to sending parameters

jsp:include tag : include a resource at runtime

jsp:forward tag: forward the control to specific resource

jsp:plugin tag : to plugin a web resource url applet

Directives:

These tags effect the overall structure of the servlet that result from translation. 3 types of directives are defined.

Page directive: used to define and manipulate the no. of page dependent attributes that effect the whole jsp.

include directive: This instructs the container to include the content of the resource in the current jsp this file is parsed once, when translation is done.

Taglib directive: To use tag extentions to define custom tags.

Scriptlets: There are used to include javacode in jsp page these are of 3 types

scriptlet: used to write pure java code

declarations: used to declare java variables and methods

Expressions: These send the value of a java expression back to client. These results are converted to string and displayed at client.

15) jsp:useBean tag and it's properties?

To separate the code from the presentation it would be good idea to encapsulate the code in java object instantiate it and use it in our jsp. This instance is varaible is called 'id'.We can also specific life time of this object by using 'scope' attribute

jsp:useBean id='name' scope=”scope” class=”beanclass”/

Properties:

id: a case sensitive name is used.

Scope: The scope with in which the reference is available. page, request,session, application are possible values page is default

class: the fully qulified classes name

beanname: The name of the java beanclass

type: This type must be super class of the beans classes

16)How do you implement Singe Thread Model in JSP?

By simply include a page directives tag

%@page isThreadSafe=”false” %

17)How do you declare a page as Error Page. What tag you include in a JSP page so that it goes to specified error page in case of an exception?

By including a page directive tag %@ page isErrorPage=”true”%

then this page is including a page directive in our jsp pages

%@page errorpage=”url of the above jsp”% tag

calling this page is including a page directive in our jsp page

%@page errorpage=”url of the above jsp”%

18)What is Request Dispatcher? How do you get it?

The name itself reveals that it is used to dispatch the control to requesting resource. It is an interface used to include any resource with in our servlet or forward the controler to any other resource. It contains two methods.

Forward(“---url”);

forward(“---url”);

For getting this we have a method in servlet context interface. So we can get it by servlet context object

sc.getRequestDispatcher();

19) Difference between JSP & Servlets?

Both are web applications used to produce web content that means dynamic web pages. Bot are used to take the requests and service the clients. The main difference between them is, In servlets both the presentation and business logic are place it together. Where as in jsp both are separated by defining java beans .

In jsp's the overall code is modulated so the developer who deesn't know about java can write jsp pages by simply knowing the additional tages and class names.

One more important to be considered is servlet take less time to compile. Jsp is a tool to simplify the process and make the process automate.

20)Difference between Hashtable & HashMap?

Hash table is a Collection of objects .To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode method and the equals method. Hashtable is Sychronized and permit non- null values only.

Hashtable maps keys to values. Any non-null object can be used as a key or as a value.

The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.

Goto part 2

Sun GlassFish Enterprise Server

2009-10-14T03:51:00.000-07:00

The Sun GlassFish Enterprise Server provides the foundation to develop and deploy Java EE artifacts, including Web Services. It provides value-added services for management, monitoring, diagnostics, clustering, transaction management and high availability of mission-critical services.The Features and Benefits are as follows:

GlassFish v3 Preview

Java EE 6 - Includes new and updated specifications, includes Web Profile distribution
OSGi Runtime - Dynamically extensible, lightweight runtime platform that consumes minimal resources
Improved Administration - Extensible administration (add custome features/commands), RESTful administration API
Embedded API - Easily embed GlassFish Enterprise Server v3 in your solution
Enhanced monitoring - Enables more granular monitoring with less overhead; includes Dtrace integration on Solaris

Java EE Compatible

Implements Java EE 5, which helps improve developer efficiency
Enterprise Java Beans 3.0 reduces the amount of code required by as much as 30 to 90%
A new Persistence API allows maximum flexibility in specifying the mapping of Java business objects to a relational database
Java Server Faces 1.2 simplifies the building of user interfaces for Web-based applications
Use of Annotations reduces the need to edit and maintain separate files during development

Dynamic language support

Enables deployment of JRuby and Groovy applications

Rapid iterative development features

Simplifies development lifecycle of Java Web applications to "edit-save-refresh browser" by maintaining servlet session state after application redeploy

Clustering for scalability and high availability

Create and manage clusters from a single administration console and manage a cluster as a single entity
Dynamically grow or shrink a cluster by adding or removing application server instances
Load-balancing plugin monitors cluster health and balances load across available instances
Automatically update the load-balancing plugin

Breakthrough performance

GlassFish is the fastest open-source application server, surpassing the industry's leading application servers
GlassFish is highly scalable and optimized for multi-core servers, including Sun servers with CoolThreads technology
Fast Infoset support improves Web services performance by a magnitude of 2x to 4x, with Sun's Project Metro JAX-WS surpassing other implementations

Open source foundation

GlassFish Enterprise Server is based on Project GlassFish

Sophisticated administration

Centralized administration of deployed instances and clusters
Provides remote secure management using a browser-based admin console and a feature-equivalent scriptable command-line interface
Enhanced application monitoring, visualization, and diagnosis
Built-in management rules and triggers can be expanded programmatically

Integrated development support

Includes NetBeans and Eclipse IDE support; refer to the GlassFish Plugins project

.NET 3.0 Web services interoperability

Leveraging Project Metro (see above), Sun's Web Services stack, applications can interoperate with Windows Communication Foundation(WCF)

Update Center

Quick access to new technologies such as Open ESB, jMaki, JRuby, additional samples and documentation

Improves developer productivity

Provides simplified Java EE APIs and annotations, reducing the amount of code a developer needs to write by up to 78%
Can speed start-up by up to 30% (on-demand initialization) and reduce memory requirements by up to 30%
Java EE 5 SDK bundles GlassFish Enterprise Server, Netbeans, and Open ESB for building SOA components, managing a Web services stack, and providing a framework for a Federated Identity management system

Java EE 5 Certified Application Servers

2009-10-14T02:11:00.000-07:00

Sun Java System Application Server Platform Edition 9.0, based on the open-source server GlassFish
GlassFish
JBoss Application Server Version 5.1.2
JOnAS an open-source application server from OW2 Consortium
Apache Geronimo 2.0
Apache OpenEJB via Apache Geronimo
IBM WebSphere Application Server Community Edition 2.0, based on Apache Geronimo
IBM WebSphere Application Server V7
WebLogic Application Server 10.0 from Oracle
Oracle Containers for Java EE 11
SAP NetWeaver Application Server, Java EE 5 Edition from SAP
JEUS 6, an application server from TmaxSoft

Introduction to JEE,Various types of APIs in JEE

2009-10-13T23:43:00.000-07:00

Java Platform Enterprise Edition or Java EE is a widely used platform for server programming in the Java programming language. The Java Platform (Enterprise Edition) differs from the Java Standard Edition Platform (Java SE) in that it adds libraries which provide functionality to deploy fault-tolerant, distributed,multi-tier Java software, based largely on modular components running on an application server.

The Java EE APIs includes several technologies that extend the functionality of the base Java SE APIs.

javax.ejb --The Enterprise JavaBean's 1st and 2nd API defines a set of APIs that a distributed object container will support in order to provide persistence, remote procedure calls (using RMI or RMI-IIOP), concurrency control, and access control for distributed objects. This package contains the Enterprise JavaBeans classes and interfaces that define the contracts between the enterprise bean and its clients and between the enterprise bean and the ejb container.abd.

javax.transaction--These packages define the Java Transaction API.

javax.xml.stream--This package contains readers and writers for XML streams.

javax.jms--This package defines the Java Message Service(JMS) API.The JMS API provides a common way for Java programs to create, send, receive and read an enterprise messaging system's messages.

javax.resource--This package defines the Java Enterprise Edition Connector Architecture API. Java EE Connector Architecture (JCA) is a Java-based technology solution for connecting application servers and enterprise information systems (EIS) as part of enterprise application integration (EAI) solutions.

javax.faces.component.html--This package defines the JavaServer Faces(JSF) API. JSF is a technology for constructing user interfaces out of components.

javax.persistence--This package contains the classes and interfaces that define the contracts between a persistence provider and the managed classes and the clients of the Java Persistence API.