Inheritance
Inheritance enables programmers to define an "is-a"
relationship between a class and a more specialized version of that
class. For example, if a Student class extends a Person class, then it should be
the case that Student is-a Person. The subclass Student builds on the
functionality of the superclass Person. Object-oriented programming allows
classes to inherit commonly used state and behavior from other classes. In the
Java programming language, each class is allowed to have one direct superclass,
and each superclass has the potential for an unlimited number of subclasses.The
syntax for creating a subclass is simple. At the beginning of your class
declaration, use the extends keyword, followed by
the name of the class to inherit from.
class auto extends
vehicle
Constructor
A constructor creates an Object of the class that it is in by initializing
all the instance variables and creating a place in memory to hold the Object. It
is always used with the keyword new and then the Class name. For instance,
new String(); constructs a new String object.
Sometimes in a few classes you may have to initialize a few of the variables to
values apart from their predefined data type specific values. If Java
initializes variables it would default them to their variable type specific
values. For example you may want to initialize an integer variable to 30 or 40
based on a certain condition, when your class is created. In such a case you
cannot hard code the value during variable declaration. Such kind of code can be
placed inside the constructor so that the initialization would happen when the
class is instantiated.
Now we are going to develop an application to describe the concept that how to
work with these two concept. For this we should follow the following step.
Step 1: Creating a new project.
This is the first application, in this step we select the New Project option
from File menu
![create new project.jpg]()
Step 2: Select Application Type
In this step we select web application option from Java web and then click
on the next button.
![select new web application.jpg]()
Step 3: Name and Location.
In this step we give it a specific name InheritanceJsp and select a specific
location for it and then click on the next button.
![name and location.jpg]()
Step 4: Server and Setting.
In this step we select a specific server glassfis and configure it.
![server and setting.jpg]()
Step 5: Select Framework.
There is no need to select any framework for this aplication.
![selectframework.jpg]()
Step 6: Create new JSP file.
In this application we create two JSP file (useinheritance.jsp
and useconstructor.jsp)
![create new jsp file.jpg]()
UseInheritance.jsp
<HTML>
<HEAD>
<TITLE>Inheritance in JSP</TITLE>
</HEAD>
<BODY BGCOLOR="cyan">
<H1>Inheritance in
JSP</H1>
<%!
javax.servlet.jsp.JspWriter localelement;
class vehicle
{
public void start() throws
java.io.IOException
{
localelement.println("Starting Any Vechicle<BR>");
}
}
class automobile extends vehicle
{
public void drive() throws
java.io.IOException
{
localelement.println("Driving The car First<BR>");
}
}
%>
<%
localelement = out;
out.println("Creating an automobile...<BR>");
automobile a = new automobile();
a.start();
a.drive();
%>
</BODY>
</html>
UseConstructor.jsp
<HTML>
<HEAD>
<TITLE>Constructors and Inheritance In JSP</TITLE>
</HEAD>
<BODY BGCOLOR="skyblue">
<H1>Constructors and Inheritance In JSP</H1>
<%!
javax.servlet.jsp.JspWriter localelement;
class A
{
A() throws java.io.IOException
{
localelement.println("In A\'s
constructor<BR>");
}
A(String s) throws java.io.IOException
{
localelement.println("In A\'s
String constructor<BR>");
localelement.println(s);
}
}
class B extends A
{
B(String s) throws java.io.IOException
{
super(s);
localelement.println("In B\'s String
constructor<BR>");
localelement.println(s);
}
}
%>
<%
localelement = out;
B obj = new B("Hello from JSP
Constructor<BR>");
%>
</BODY>
</HTML>
Step 7: Compiling and running the application.
After completion of the coding part now compile it for the first time and then run it
on the specific web server and find the output.
Output
UseInheritance.jsp
![useinheritence.jsp.jpg]()
UseConstructor.jsp
![Useconstructor.jsp.jpg]()
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