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Working With an Abstract Class in JSP

Posted by Vikas Mishra Articles | JSP December 14, 2011
Java provides a special type of class called an abstract class which helps us to organize our classes based on common methods. An abstract class lets you put the common method names in one abstract class without having to write the actual implementation code.
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Introduction

Java provides a special type of class called an abstract class which helps us to organize our classes based on common methods. An abstract class lets you put the common method names in one abstract class without having to write the actual implementation code. In another words we can say that an abstract class is a class that is declared by using the abstract keyword
. It may or may not have abstract methods. Abstract classes cannot be instantiated, but they can be extended into sub-classes.


Why We Use Abstract Classes: There are situations in which you will want to define a super class that declares the structure of a given abstraction without providing a complete implementation of every method. That is, sometimes you will want to create a super class that only defines a generalized form that will be shared by all of its subclasses, leaving it to each subclass to fill in the details. Such a class determines the nature of the methods that the subclasses must implement. One way this situation can occur is when a superclass is unable to create a meaningful implementation for a method. This is the case with the class Figure used in the preceding example. The definition of area( ) is simply a placeholder. It will not compute and display the area of any type of object.
As you will see as you create your own class libraries, it is not uncommon for a method to have no meaningful definition in the context of its superclass. You can handle this situation two ways. One way, as shown in the previous example, is to simply have it report a warning message. While this approach can be useful in certain situations—such as debugging—it is not usually appropriate. You may have methods which must be overridden by the subclass in order for the subclass to have any meaning. Consider the class Triangle. It has no meaning if area( ) is not defined. In this case, you want some way to ensure that a subclass does, indeed, override all necessary methods. Java's solution to this problem is the abstract method.

An application of abstract class with JSP: Here we are going to prepare an application of abstract class with JSP , we using NetBeans IDE(7.0) for it.

Step 1 : Creating a new project: In this step we click on the file menu and select New Project option:

1..gif

Step 2 : Choosing Project: In this step we select the project type. We select java web application and click on the Next button:

selectproject.gif

Step 3 : Name and Location: In this step we give it a specific name UsingAbstractionJsp and also give it a specific loccation:

namingand-location.gif

Step 4 : Select a Server and provide it a setting: In this step we select GlassFish Server 3.1 version (java EE 6 web) and Set the context path:

server-and-setting.gif

Step 5 : Select Framework: There is no need to select any framework just click on the Finish button:

framework.gif

Step 5 : Choose File: In this step we choose an jsp file and starts coding on it:

then-coding.gif

Index.jsp File: In this file we create an abstact class M, it has a abstract method. We provide body to it in another class N.

<HTML>
<HEAD>

<TITLE>Using Abstract Classes In JSP</TITLE>
</HEAD>

<BODY bgcolor="green">
<H1>Using Abstract Classes In JSP</H1>
<%!
javax.servlet.jsp.JspWriter localOut;
abstract class M
{
abstract String getText() throws java.io.IOException;
public void printem() throws java.io.IOException
{
localOut.println(getText());
}
}
class N extends M
{
String getText() throws java.io.IOException
{
return "Hello from JSP!<br/> My Name Is:Vikas<br/>My Title Is:Mishra";
}
}
%>
<%
localOut = out;
N nObject = new N();
nObject.printem();
%>
</BODY>
</HTML>


Step 6 : Compile and Run File:
After completion Compile it and run it on the any browser :

Output: Then it will give the following output:

output.gif

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