队列，先进先出结构

增

public void offer(E data){
   
        Node<E> node  = new Node<>(data);
        if (head.next == null) {
   
            rear = head;
        }
        while (rear.next != null){
   
           rear = rear.next;
        }
        rear.next = node;
        rear = node;
        rear.next = null;
    }

删

 public E poll(){
   
        if (isEmpty()){
   
            throw new RuntimeException("队列为空");
        }
        E e = head.next.data;
        head.next = head.next.next;
        return e;
    }

查

  public E peek(){
   
        if (isEmpty()) {
   
            throw new RuntimeException("队列为空");
        }
        return head.next.data;
    }

总览

package com.collection;

/**
 * @author WangYH
 * @version 2021.1.3
 * @date 2023/4/30 9:50
 */

public class LinkedQueue<E> {
   

    private Node<E> head = new Node<>(null);
    private Node<E> rear = new Node<>(null);


    public void offer(E data){
   
        Node<E> node  = new Node<>(data);
        if (head.next == null) {
   
            rear = head;
        }
        while (rear.next != null){
   
           rear = rear.next;
        }
        rear.next = node;
        rear = node;
        rear.next = null;
    }

    public E poll(){
   
        if (isEmpty()){
   
            throw new RuntimeException("队列为空");
        }
        E e = head.next.data;
        head.next = head.next.next;
        return e;
    }

    public E peek(){
   
        if (isEmpty()) {
   
            throw new RuntimeException("队列为空");
        }
        return head.next.data;
    }

    public boolean isEmpty() {
   
        return head.next == null;
    }

    private static class Node<E> {
   
        private E data;
        private Node<E> next;

        public Node(E data) {
   
            this.data = data;
        }
    }
}

测试

package com.collection;

/**
 * @author WangYH
 * @version 2021.1.3
 * @date 2023/4/29 21:42
 */

public class Main {
   
    public static void main(String[] args) {
   
       LinkedQueue<String> queue = new LinkedQueue<>();
       queue.offer("A");
       queue.offer("B");
       queue.offer("C");
       queue.offer("D");

        System.out.println(queue.peek());
        while (!queue.isEmpty()) {
   
           System.out.println(queue.poll());
       }

    }
}