LinkedListQueue.java

import java.security.PublicKey;

/**
 * LinkedListQueue
 *
 * @author LiYang
 * @date 2020/1/8
 **/
public class LinkedListQueue<E> implements Queue<E> {
    private class Node{
        public E e;
        public Node next;

        public Node(E e, Node next){
            this.e = e;
            this.next = next;
        }

        public Node(E e) {
            this.e = e;
            next = null;
        }

        public Node(){
            e = null;
            next = null;
        }

        @Override
        public String toString() {
            return e.toString();
        }

    }

    private Node head, tail;   // 指向功能
    private int size;

    public LinkedListQueue() {
        head = null;
        tail = null;
        size = 0;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    @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++;
    }

    @Override
    public E dequeue() {
        if (isEmpty())
            throw new IllegalArgumentException("Cannot dequeue from an empty queue");
        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if (head == null)
            tail = null;
        size--;
        return retNode.e;
    }

    @Override
    public E getFront() {
        if (isEmpty())
            throw new IllegalArgumentException("Cannot getFront from an empty queue");
        return head.e;
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append("LinkedListQueue front ");
        Node cur = head;
        while (cur != null) {
            res.append(cur + "->");
            cur = cur.next;
        }
        res.append("Null tail");
        return res.toString();
    }

    public static void main(String[] args) {
        LinkedListQueue<Integer> queue = new LinkedListQueue<>();
        for (int i = 0; i < 10; i++) {
            queue.enqueue(i);
        }
        System.out.println(queue);
        queue.enqueue(5);
        System.out.println(queue);
        System.out.println(queue.dequeue());
        System.out.println(queue);
        System.out.println(queue.getFront());
        System.out.println(queue);
    }
}