队列

实现队列

/*
*路人假helloWorld
*/
package com.cjj.sort;

import java.util.Iterator;

public class Queue<T> implements Iterable<T>{
    private Node head;
    private int N;
    private Node last;

    //内部结点类
    private class Node{
        public T item;
        public Node next;

        public Node(T item,Node next){
            this.item = item;
            this.next = next;
        }
    }

    public Queue(){
        this.head = new Node(null,null);
        this.last = null;
        this.N = 0;
    }

    //判断队列是否为空
    public boolean isEmpty(){
        return N == 0;
    }

    //获取队列元素的个数
    public int size(){
        return N;
    }

    //往对列中插入一个元素
    public void enqueue(T t){
        Node newNode = new Node(t,null);
        if (last == null){
            last = newNode;
            head.next = last;
        }else{
            last.next = newNode;
            last = newNode;
        }
        N++;
    }

    //往队列中拿出一个元素
    public T dequeue(){
        Node oldFirst;
        if (isEmpty()){
            return null;
        }
        oldFirst = head.next;
        head.next = oldFirst.next;
        N--;
        return oldFirst.item;
    }

    @Override
    public Iterator<T> iterator() {
        return new QIterator();
    }

    private class QIterator implements Iterator{
        Node n;

        public QIterator(){
            n = head;
        }

        @Override
        public boolean hasNext() {
            return n.next != null;
        }

        @Override
        public Object next() {
            n = n.next;
            return n.item;
        }
    }
}

测试

package com.cjj.test;

import com.cjj.sort.Queue;

public class QueueTest {
    public static void main(String[] args) {
        Queue<String> q = new Queue<>();
        q.enqueue("a");
        q.enqueue("b");
        q.enqueue("c");
        q.enqueue("d");

        for (String item : q){
            System.out.println(item);
        }

        System.out.println("----------------------");

        System.out.println("取出的第一个队列元素是：" + q.dequeue());
        System.out.println("队列中还剩几个元素：" + q.size());
    }
}