6、队列的链式存储、含首尾指针的单链表

package ren.laughing.datastructure.baseImpl;

import ren.laughing.datastructure.base.Queue;
import ren.laughing.datastructure.exception.QueueEmptyException;
/**
 * 队列的链式存储
 * 单链表、含有队首和队尾指针
 * @author Laughing_Lz
 * @time 2016年4月7日
 */
public class QueueLinked implements Queue {
    private SLNode front;//队首指针，指向链表空的头结点
    private SLNode rear;//队尾指针，指向链表的队尾元素
    private int size;//队的容量
    
    public QueueLinked() {
        front = new SLNode();
        rear = front;//队列初始为空，队首指针和队尾指针均指向空的头结点
        size = 0;
    }
    
    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }
    //入队：从队尾入队,相当于insertAfter队尾结点rear
    @Override
    public void enqueue(Object e) {
        SLNode node =new SLNode(e, null);//写出rear.getNext()应该也可以？
        rear.setNext(node);
        rear = node;
        size++;
    }
    //出队：从队首出队，相当于removeAfter队首头结点front
    @Override
    public Object dequeue() throws QueueEmptyException {
        if(size <= 0){
            throw new QueueEmptyException("错误：队列为空");
        }
        SLNode node = front.getNext();//要删除的队首数据元素
        front.setNext(node.getNext());
        size--;
        if(size <= 0){//★再次判断size，若已全部出队，则将rear指针也和front指针一样指向空的头结点
            rear = front;
        }
        return node.getData();
    }
    
    @Override
    public Object peek() throws QueueEmptyException {
        if(size <= 0){
            throw new QueueEmptyException("错误：队列为空");
        }
        SLNode node = front.getNext();
        return node.getData();
    }

}