Partial Implementations

If a class involves an interface but does not fully implement the functions defined through that interface then which class must be declared as abstract. For instance:

abstract class Incomplete implements Callback {

int a, b;

void show ( ) {

System.out.println (a+ " "  +b);

}

/ / ....

}

In the above example, the class Incomplete does not implement callback ( ) and must be declared as abstract. Any class which inherits incomplete have to be implement callback (  ) or be declared abstract itself.