Java™ How To Program (Early Objects), Tenth Edition

Forming a Stack Class Via Composition Rather Than Inheritance

A better way to implement a stack class is by reusing a list class through composition. Figure 21.12 uses a private List<T> (line 7) in class StackComposition<T>’s declaration. Composition enables us to hide the List<T> methods that should not be in our stack’s public interface. We provide public interface methods that use only the required List<T> methods. Implementing each stack method as a call to a List<T> method is called delegation—the stack method invoked delegates the call to the appropriate List<T> method. In particular, StackComposition<T> delegates calls to List<T> methods insertAtFront, removeFromFront, isEmpty and print. In this example, we do not show class StackCompositionTest ...