Background

In Object$-$Oriented languages it can be useful to share code between groups of related classes. We do this via inheritance.

Both cats and dogs have names and ages, so we may wish to share this functionality in a super class.

When we do not know the default functionality we want subclasses to have, we use an abstract method. An abstract method must be implemented by its subclasses. If a class has any abstract methods, it must be declared as an abstract class.

abstract class A $\{$

public abstract int f$()$;

$\}$

class B extends A $\{$

@Override

public int f$()\{$

$//$ Implementation

$\}$

$\}$