Delegation

"In some situations, using inheritance to extend a class leads to a bad design. Though less convenient, delegation is a more general-purpose way of extending classes. Delegation succeeds in many situations where inheritance does not work well.

Inheritance is a common way to extend and reuse the functionality of a class. Delegation is a more general way for extending a class's behavior that involves a class calling another class's methods rather than inheriting them. Inheritance is inappropriate for many situations in which delegation is appropriate."

Ref. Mark Grand, Patterns in Java Vol I.