Java使用链表(无虚拟头结点,有尾节点)实现队列
接口interface Queue<E>
public interface Queue<E> {
int getSize();
boolean isEmpty();
void enqueue(E e);//入队
E dequeue();//出队
E getFront();//获得队首元素
}
使用链表实现接口并测试
/**
* @author yinglongwu
*/
//使用带尾节点的链表实现队列
//从head端删除元素(队首),从tail端插入元素(队尾)
public class LinkedListQueue<E> implements Queue<E> {
//定义链表的节点类
private class Node{
public E e;//存放这个节点的元素
public Node next;//这个节点指向的下一个节点
private Node(E e, Node next) {
this.e = e;
this.next = next;
}
public Node (E e) {
this(e,null);
}
public Node() {
this(null,null);
}
//重写toString方法,方便打印节点的信息
@Override
public String toString() {
return e.toString();
}
}
private Node head,tail; //添加一个尾节点变量,便于实现队列
private int size;
//无参构造
public LinkedListQueue() {
head = null;
tail = null;
size = 0;
}
@Override
public int getSize() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
//入队,从链表尾部
@Override
public void enqueue(E e) {
if (tail == null) {
tail = new Node(e);
head = tail;
} else {
tail.next = new Node(e);
tail = tail.next;
}
size++;
}
//出队,从链表头部
@Override
public E dequeue() {
if (isEmpty()) {
throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
}
Node retNode = head;//存放要被删除的头结点
head = head.next; //新的头结点
retNode.next = null;
if (head == null) { //如果新的头结点为空,那么尾节点也应该为空
tail = null;
}
size--;
return retNode.e;
}
//获取队首元素
@Override
public E getFront() {
if (isEmpty()) {
throw new IllegalArgumentException("Queue is empty.");
}
return head.e;
}
//重写toString方法,便于打印
@Override
public String toString() {
StringBuilder res = new StringBuilder();
res.append("Queue: front ");//队首
Node cur = head;
while (cur != null) {
res.append(cur + "->");
cur = cur.next;
}
res.append("NULL tail");//队尾
return res.toString();
}
//测试
public static void main(String[] args) {
LinkedListQueue<Integer> queue = new LinkedListQueue<Integer>();
for (int i = 0; i < 10; i++) {
queue.enqueue(i);//入队
System.out.println(queue);
if (i%3==2) {//每三个元素出队一次
queue.dequeue();
System.out.println(queue);
}
}
}
}
输出结果