java 数据结构 队列的实现

/**
 * java数据结构之队列的实现
 * 2016/4/27
 **/
package cn.Link;
import java.util.*;

public class Queue{
    Node tail = new Node(); 
    Node nowNode = new Node();   //永远指向队首
    int size;
    Queue(){};
    Queue(String date){
        this.tail.date = date;
        this.tail.next = null;
        this.nowNode.next = this.tail;
        this.size = 1;
        System.out.println("队列已经被建立，"+date+"被加入到队列中");
    }

    //节点类
    class Node{
        String date;
        Node next;
        Node(){};
        Node(String date){
            this.date = date;
        }
    }

    //向队列中插入数据
    public void EnQueue(String date){
        Node preNode = new Node(date);
        preNode.next = this.nowNode.next;
       this.nowNode.next = preNode; 
       this.size++;
       System.out.println("数据"+date+"被加入到队列中");
    }

    //出队列操作
    public void DeQueue(){
        Node preNode = new Node();
        preNode.next = this.nowNode.next;
        while(true){
            if(preNode.next.next != this.tail){
                preNode.next = preNode.next.next;
            }else{
                preNode.next.next = null;
                this.tail = preNode.next;
                System.out.println("出队列完成～～～"); break;
            }
        }
        this.size--;
    }

    //遍历队列输出
    public void PrintQueue(){
        Node preNode = new Node();
        preNode.next = this.nowNode.next;
        System.out.print("遍历输出队列： ");
        while(preNode.next != null){
            System.out.print(" -->"+preNode.next.date);
            preNode.next = preNode.next.next;
        }
        System.out.println("+++++++++++当前队列的长度为"+this.size);
    }

    //清空队列
    public void clear(){
        this.nowNode.next = null;
        this.tail = null;
        this.size = 0;
        System.out.println("队列已被清空");

    }

    public static void main(String[] args){
        Queue queue = new Queue("sum1");
         queue.EnQueue("sum2");
         queue.EnQueue("sum3");
         queue.EnQueue("sum4");
         queue.EnQueue("sum5");
         queue.EnQueue("sum6");
         queue.EnQueue("sum7");
         queue.EnQueue("sum8");
         queue.PrintQueue();
         queue.DeQueue();
         queue.DeQueue();
         queue.PrintQueue();
    }
}