Explain Inheritance In Java With Program And Examples, Inheritance Program With Explanation
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Inheritance Basics
To inherit a class, you simply incorporate the definition of one class into another by using
the
extends
keyword. To see how, let’s begin with a short example. The following program
creates a superclass called
A
and a subclass called
B
. Notice how the keyword
extends
is
used to create a subclass of
A
.
// A simple example of inheritance.
// Create a superclass.
class A {
int i, j;
void showij() {
System.out.println("i and j: " + i + " " + j);
}
}
// Create a subclass by extending class A.
class B extends A {
int k;
void showk() {
System.out.println("k: " + k);
}
void sum() {
System.out.println("i+j+k: " + (i+j+k));
}
}
157
class SimpleInheritance {
public static void main(String args[]) {
A superOb = new A();
B subOb = new B();
// The superclass may be used by itself.
superOb.i = 10;
superOb.j = 20;
System.out.println("Contents of superOb: ");
superOb.showij();
System.out.println();
/* The subclass has access to all public members of
its superclass. */
subOb.i = 7;
subOb.j = 8;
subOb.k = 9;
System.out.println("Contents of subOb: ");
subOb.showij();
subOb.showk();
System.out.println();
System.out.println("Sum of i, j and k in subOb:");
subOb.sum();
}
}
The output from this program is shown here:
Contents of superOb:
i and j: 10 20
Contents of subOb:
i and j: 7 8
k: 9
Sum of i, j and k in subOb:
i+j+k: 24
As you can see, the subclass
B
includes all of the members of its superclass,
A
. This is
why
subOb
can access
i
and
j
and call
showij( )
. Also, inside
sum( ) i
,
and
j
can be referred
to directly, as if they were part of
B
.
Even though
A
is a superclass for
B
, it is also a completely independent, stand-alone
class. Being a superclass for a subclass does not mean that the superclass cannot be used
by itself. Further, a subclass can be a superclass for another subclass.
The general form of a
class
declaration that inherits a superclass is shown here:
class subclass-name extends superclass-name {
// body of class
}
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Part I:
The Java Language
You can only specify one superclass for any subclass that you create. Java does not
support the inheritance of multiple superclasses into a single subclass. You can, as stated,
create a hierarchy of inheritance in which a subclass becomes a superclass of another subclass.
However, no class can be a superclass of itself.