1. /**
    2.  * @author luobo.cs@raycloud.com
    3.  * @since 2021/7/25 10:47 上午
    4.  */
    5. public class LinkedListQueue<E> {
    8.     private int size = 0;
    9.     private Node<E> head;
    10.     private Node<E> tail;
    12.     public LinkedListQueue() {
    13.         head = new Node<>();
    14.         tail = new Node<>();
    15.         head.next = tail;
    16.         head.prev = tail;
    18.         tail.next = head;
    19.         tail.prev = head;
    20.     }
    22.     public int size() {
    23.         return size;
    24.     }
    26.     public void push(E e) {
    27.         final Node<E> temp = new Node<>();
    29.         //1、获取尾节点的前一个节点
    30.         final Node<E> prev = tail.prev;
    31.         //2、修改尾部指向
    32.         prev.next = temp;
    33.         tail.prev = temp;
    34.         //3、修改当前节点指向
    35.         temp.next = tail;
    36.         temp.prev = prev;
    37.         temp.data = e;
    38.         size++;
    39.     }
    41.     public E poll() {
    42.         final Node<E> next = head.next;
    43.         if (next.equals(tail)) {
    44.             return null;
    45.         }
    46.         final E data = next.data;
    47.         head = next;
    48.         size--;
    49.         return data;
    50.     }
    52.     private static class Node<E> {
    53.         public Node<E> prev;
    54.         public Node<E> next;
    55.         private E data;
    56.     }
    58.     public static void main(String[] args) {
    59.         LinkedListQueue<String> queue = new LinkedListQueue<>();
    60.         queue.push("111");
    61.         queue.push("222");
    62.         queue.push("333");
    63.         queue.push("444");
    64.         System.out.println(queue.size);
    65.         System.out.println(queue.poll());
    66.         System.out.println(queue.poll());
    67.         System.out.println(queue.poll());
    68.         System.out.println(queue.poll());
    69.         System.out.println(queue.poll());
    70.         System.out.println(queue.size);
    72.     }
    73. }