Inheritance

Methods a Subclass Must Override

Subclass must override methods that are declared abstract in the superclass, or the subclass itself must be abstract.

ABSTRACT CLASSES

Abstract classes are those which can be used for creation of objects. However their methods and constructors can be used by the child or extended class. The need for abstract classes is that you can generalize the super class from which child classes can share its methods. The subclass of an abstract class which can create an object is called as "concrete class".

Following is an example

Abstract class A
{
abstract void method1();
void method2()
{
System.out.println("this is concrete method");
}
}
class B extends A
{
void method1()
{
System.out.println("B is implementation of method1");
}
}
class demo
{
public static void main(String arg[])
{
B b=new B();
b.method1();
b.method2();
}
}