数据结构实现Java版-队列（链表实现）

接口

public interface Queue {
    void enqueue(E e);
    E dequeue();
    E getFront();
    int getSize();
    boolean isEmpty();
}

实现

public class LinkedListQueue implements Queue {
    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,null);
        }
        public Node(){
            this(null,null);
        }

        @Override
        public String toString() {
            return e.toString();
        }
    }
    private Node head,tail;
    private int size;
    public LinkedListQueue(){
        head=null;
        tail=null;
        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("Queue is empty ");
        }
        return head.e;
    }

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

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

    @Override
    public String toString() {
        StringBuilder res =new StringBuilder();
        res.append("Queue: 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 queue =new LinkedListQueue<>();
        for (int i = 0; i < 10; i++) {
            queue.enqueue(i);
            System.out.println(queue);
            if(i%3==2){
                queue.dequeue();
                System.out.println(queue);
            }
        }
    }
}