这里采用的是双端链表来实现的先进先出对列。

package com.yanling.queue;

/**
 * 队列（先进先出）
 * @author yanling
 * @date 2021-2-14
 */
public class MyFIFO {

    public int size;
    /**
     * 尾指针
     */
    private Node last;
    /**
     * 头指针
     */
    private Node first;

    /**
     * 队列添加元素
     * @param e
     */
    public void add(int e) {
        Node f = last;
        Node newNode = new Node(f, e, null);
        last = newNode;
        if (f == null) {
            first = newNode;
        } else {
            f.gNext = last;
        }
        size++;
    }

    /**
     * 弹出第一个元素
     * @return
     */
    public Integer poll(){
        if (first == null) {
            return null;
        }
        Node team = first;
        first = first.gNext;
        if (first != null) {
            // 断开连接
            first.lNext = null;
        }
        size--;
        return team.val;
    }

    /**
     *  双向链表
     */
    class Node {

        int val;
        Node lNext;
        Node gNext;

        public Node(Node lNext, int val, Node gNext) {
            this.val = val;
            this.lNext = lNext;
            this.gNext = gNext;
        }
    }
}

完成了对列的实现，线面测试下

    public static void main(String[] args) {
        MyFIFO fifo = new MyFIFO();
        fifo.add(1);
        fifo.add(2);
        fifo.add(3);
        for (; 1 < fifo.size;) {
            System.out.println(fifo.poll());
        }
        fifo.add(4);
        fifo.add(5);
        for (; 0 < fifo.size;) {
            System.out.println(fifo.poll());
        }
        System.out.println(fifo.poll());
    }

控制台打印结果