Java How To Program, Late Objects, 11th Edition

... interface. Using composition enables us to hide class List<E>’s other public methods from Queue<E>’s client code. Each Queue<E> method delegates to a List<E> method—enqueue calls List<E> method insertAtBack (Fig. 21.11, line 14), dequeue calls List<E> method removeFromFront (line 18), isEmpty calls List<E> method isEmpty (line 22) and print calls List<E> method print (line 25). For reuse, class Queue<E> is declared in package com.deitel.datastructures. Again, we do not import List<E> because it’s in the same package.

Fig. 21.11 Queue uses class List.

 1   // Fig.  21.11: Queue.java
 2   // Queue uses class List.
 3   package com.deitel.datastructures;
 4
 5   import java.util.NoSuchElementException;
 6
 7   public class Queue<E> {
 8      private List<E> queueList;
 9
10      // ...