先看队列接口和结点类

package com.lovely.queue;/** * 2020年4月26日下午2:42:44* * @author echo lovely**/
public interface IQueue {public void clear(); // 将队列置空public boolean isEmpty(); // 判断队列是否为空public int length(); // 返回队列的数据元素个数public Object peek(); // 返回队首元素 public void offer(Object x) throws Exception; // x插入队列，队尾入队public Object poll(); // 返回队首元素，并删除 队首出队public void display(); // 输出队列中所有数据元素}package com.lovely.linearList;/** * 2020年4月1日下午8:25:10* * @author echo lovely** @category 节点类 用于存数据 和 后继节点*/public class Node {public Object data; // 存放节点数据值public Node next; // 存放后继节点public Node() {this(null, null);}// 只有节点值的构造函数public Node(Object data) {this(data, null);}// 带有节点值和后继节点的构造函数public Node(Object data, Node next) {this.data = data;this.next = next;}
}

1. 顺序队列

package com.lovely.queue;/*** @author echo lovely** 2020年4月26日下午3:03:05* * 队列的顺序储存结构* 队首出队（删除），队尾入队（插入）。*/
public class SeqQueue implements IQueue {private Object[] queueElem; // 队列的储存空间private int maxSize; // 队列的最大储存单元个数private int front; // 指向队首元素private int rear; // 指向队尾元素的下一个元素	// 构造最大储存单元为maxSize的空队列public SeqQueue(int maxSize) {this.maxSize = maxSize;front = rear = 0;queueElem = new Object[maxSize];}@Overridepublic void clear() {// 队列置空front = rear = 0;	}@Overridepublic boolean isEmpty() {// 队列是否为空		return front == rear;}@Overridepublic int length() {// 队列长度return rear - front;}@Overridepublic Object peek() {// 返回队首元素if (isEmpty())return null;return queueElem[front];}@Overridepublic void offer(Object x) throws Exception {// 队尾入队if (rear == maxSize)throw new Exception("队列已满");queueElem[rear] = x;rear ++; // 指向队尾的下一个元素}@Overridepublic Object poll() {// 出队 只不过是不显示罢了if (isEmpty())return null;front ++; // 指向原来队首元素的下一个元素return queueElem[front];}@Overridepublic void display() {if (!isEmpty()) {for (int i = front; i < rear; i++) {System.out.print(queueElem[i] + "\t");}} elseSystem.out.println("队列为空！");}}

• 测试

package com.lovely.queue;public class TestSeqQueue {public static void main(String[] args) {// 顺序队列SeqQueue sq = new SeqQueue(6);try {// 入队sq.offer(1);sq.offer(2);sq.offer(3);sq.offer(4);} catch (Exception e) {e.printStackTrace();}System.out.println("队列长度 " + sq.length());Object obj = sq.poll();System.out.println(obj + "出队后，长度 " + sq.length());System.out.println("队首元素：" + sq.peek());sq.display();/*		这里有问题，多次入队出队操作，造成有存储空间却不能进行入队操作的"假溢出"现象try {sq.offer(88);sq.offer(88);sq.poll();sq.poll();sq.offer(88);sq.poll();} catch (Exception e) {e.printStackTrace();}System.out.println("\n长度 " + sq.length());sq.display();*//*
队列长度 4
2出队后，长度 3
队首元素：2
2	3	4
*/}}

2. 循环队列

package com.lovely.queue;/*** * @author echo lovely** 2020年5月19日下午8:53:03* * 循环顺序队列* 顺序队列的多次入队和出队 会造成有储存空间 却不能进行入队操作的假溢出现象。*/
public class CircleSeqQueue {private Object[] queueElem; // 队列的储存空间private int front; // 指向队首元素private int rear; // 指向队尾元素的下一个储存元素private int maxSize; // 队列的最大储存单元个数// 构造最大储存单位个数为maxSize的空队列public CircleSeqQueue(int maxSize) {front = rear = 0;queueElem = new Object[maxSize];this.maxSize = maxSize;}// 将队列置空public void clear() {front = rear = 0;}// 判断队列是否为空public boolean isEmpty() {return front == rear;}// 队列的长度public int length() {return (rear - front + maxSize) % maxSize; }// 读取队首元素public Object peek() {if (isEmpty())return null;return queueElem[front];}// 入队public void offer(Object x) throws Exception {if ((rear + 1) % maxSize == front) throw new Exception("队列已满");queueElem[rear] = x;rear = (rear + 1) % maxSize;}// 出队public Object poll() {if (rear == front)return null;Object p = queueElem[front];front = (front + 1) % maxSize;return p;}// 遍历队列public void display() {if (!isEmpty()) {for (int i = 0; i < rear; i = (i + 1) % maxSize) {System.out.print(queueElem[i] + " ");}} elseSystem.out.println("此队列为空！");}
}

• 测试

package com.lovely.queue;public class TestCircleSeqQueue {public static void main(String[] args) {// 构造长度为10的队列CircleSeqQueue csq = new CircleSeqQueue(10);try {csq.offer(1);csq.offer(2);csq.offer(3);csq.offer(4);csq.offer(5);csq.offer(6);} catch (Exception e) {e.printStackTrace();}System.out.println("队首元素：" + csq.peek());System.out.println("出队：" + csq.poll());csq.display();}}/**
队首元素：1
出队：1
2 3 4 5 6 
*/

3. 链队列

package com.lovely.queue;import com.lovely.linearList.Node;/*** * @author echo lovely* 2020年6月7日下午7:20:02* * 链队列 * 使用单链表实现* 实现入队队尾 出队队首, 没有中间的插入或者删除* * 无需头节点 , front指向头节点 rear指向队尾结点便可*/
public class LinkQueue implements IQueue {private Node front; // 队首指针private Node rear; // 队尾指针// 构造空队列public LinkQueue() {front = rear = null;}public void clear() {front = rear = null;}public boolean isEmpty() {// 队首是否为空return front == null;}@Overridepublic int length() {Node p = front;int length = 0;while (p != null) {p = p.next;length ++;}return length;}// 返回队首元素值public Object peek() {if (isEmpty()) return null;return front.data;}@Overridepublic void offer(Object x) throws Exception {// 入队Node s = new Node(x);if (!isEmpty()) { // 队列非空rear.next = s;rear = s;} else front = rear = s;}// 出队public Object poll() {if (front == null)return null;Node p = front;front = front.next;if (p == rear) {rear = null; // 删除结点为队尾结点时需要修改rear}return p.data;}public void display() {if (!isEmpty()) {for(Node p = front;p != null;p = p.next) {System.out.print(p.data + "\t");}System.out.println();} else {System.out.println("此队列为空");}}}

• 测试

package com.lovely.queue;public class TestLinkQueue {public static void main(String[] args) {// 链队列的增删改查LinkQueue lq = new LinkQueue();try {lq.offer(2);lq.offer(3);lq.offer(5);lq.offer(7);lq.offer(11);} catch (Exception e) {e.printStackTrace();}System.out.println("入队的队列：");lq.display();System.out.println("队首元素：" + lq.peek());System.out.println("队首出队：" + lq.poll());lq.display();System.out.println("队列的长度为：" + lq.length());}}/**
入队的队列：
2	3	5	7	11	
队首元素：2
队首出队：2
3	5	7	11	
队列的长度为：4*/