IMPLEMENTING LISTS, STACKS, QUEUES, AND PRIORITY QUEUES - Introduction to Java Programming: Comprehensive Version - page 922

GenericQueue<E>

-list: java.util.LinkedList<E>

+enqueue(e: E): void
+dequeue(): E
+getSize(): int

Adds an element to this queue.

Removes an element from this queue.

Returns the number of elements in this queue.

F IGURE 24.22

GenericQueue uses a linked list to provide a first-in, first-out data structure.

L ISTING 24.7

GenericQueue.java
1 public class GenericQueue<E> {
2 private java.util.LinkedList<E> list

linked list

3 = new java.util.LinkedList<>();

4
5 public void enqueue(E e) {
6 list.addLast(e);
7 }
8
9

enqueue

public E dequeue() {

dequeue

10 return list.removeFirst();

11 }
12
13 public int getSize() {

getSize

14 return list.size();

15 }
16
17 @Override
18

public String toString() {

toString

19 return "Queue: " + list.toString();

20 }
21 }

A linked list is created to store the elements in a queue (lines 2-3). The enqueue(e)
method (lines 5-7) adds element e into the tail of the queue. The dequeue() method (lines
9-11) removes an element from the head of the queue and returns the removed element. The
getSize() method (lines 13-15) returns the number of elements in the queue.
Listing 24.8 gives an example that creates a stack using GenericStack and a queue using
GenericQueue . It uses the push ( enqueue ) method to add strings to the stack (queue) and
the pop ( dequeue ) method to remove strings from the stack (queue).
L ISTING 24.8

TestStackQueue.java
1 public class TestStackQueue {
2 public static void main(String[] args) {

3 // Create a stack

4 GenericStack<String> stack =

5 new GenericStack<>();

6
7 // Add elements to the stack
8 stack.push( "Tom" ); // Push it to the stack
9 System.out.println( "(1) " + stack);
10
11 stack.push( "Susan" ); // Push it to the the stack
12 System.out.println( "(2) " + stack);
13
14 stack.push( "Kim" ); // Push it to the stack
15 stack.push( "Michael" ); // Push it to the stack
16 System.out.println( "(3) " + stack);
17