Stacks and queues - Data Structures and Problem Solving Using Java - page 610

The ListQueue class is similar to the ListStack class. The ListQueue class skel-
eton is given in Figure 16.23. The only new thing here is that we maintain two ref-
erences instead of one. Figure 16.24 shows the constructors for the ListQueue class.

1 package weiss.nonstandard;
2
3 // ListQueue class
4 //
5 // CONSTRUCTION: with no initializer
6 //
7 // ******************PUBLIC OPERATIONS*********************
8 // void enqueue( x ) --> Insert x
9 // AnyType getFront( ) --> Return least recently inserted item
10 // AnyType dequeue( ) --> Return and remove least recent item
11 // boolean isEmpty( ) --> Return true if empty; else false
12 // void makeEmpty( ) --> Remove all items
13 // ******************ERRORS********************************
14 // getFront or dequeue on empty queue
15
16 public class ListQueue<AnyType>
17 {
18 public ListQueue( )
19 { /* Figure 16.24 */ }
20 public boolean isEmpty( )
21 { /* Figure 16.27 */ }
22 public void enqueue( AnyType x )
23 { /* Figure 16.25 */ }
24 public AnyType dequeue( )
25 { /* Figure 16.25 */ }
26 public AnyType getFront( )
27 { /* Figure 16.27 */ }
28 public void makeEmpty( )
29 { /* Figure 16.27 */ }
30
31 private ListNode<AnyType> front;
32 private ListNode<AnyType> back;
33 }

figure 16.23
Skeleton for the
linked list-based
queue class

1 /**
2 * Construct the queue.
3 */
4 public ListQueue( )
5 {
6 front = back = null;
7 }

figure 16.24
Constructor for the
linked list-based
ListQueue class