class FirstLastList_long{
	private Link_long first;
	private Link_long last;
	
	public FirstLastList_long() {			//构造函数
		this.first = null;
		this.last = null;
	}
	
	public boolean isEmpty(){
		return (first == null);
	}
	
	public void insertFirst(long dd){		//从链表的头开始插入
		Link_long newLink = new Link_long(dd);
		if(isEmpty()){
			last = newLink;				//不用改变first
		}
		newLink.next = first;
		first = newLink;
	}
	
	public void insertLast(long dd){		//从链表的尾开始插入
		Link_long newLink = new Link_long(dd);
		if(isEmpty()){
			first = newLink;			//不用改变last
		}else{
			last.next = newLink;		//在last后面添加新元素，并修改last的位置
		}
		last = newLink;					//注意：只有一个元素的时候，插入要把last也赋为newLink
	}
	
	public long deleteFirst(){
		Link_long temp = first;		//暂存first
		if(first.next == null){		//如果只有一个元素，把last也赋为null
			last = null;
		}
		first = first.next;			//把next设为first
		return temp.dData;				//返回原来的first
	}
	
	public void displayList(){
		System.out.println("List(first-->last):");
		Link_long current = first;			//用于不断改变位置实现遍历
		while(current != null){
			current.displayLink();
			current = current.next;
		}
	}
	
}

class LinkQueue{
	private FirstLastList_long theList;

	public LinkQueue() {						//构造函数
		theList = new FirstLastList_long();		//创建一个双端链表对象
	}
	
	public void push(long j){				//从链表的尾开始插入，新来的元素在尾部
		theList.insertLast(j);
	}
	
	public long pop(){
		return theList.deleteFirst();		//从链表的头开始弹出，先进的元素先被弹出
	}
	
	public boolean idEmpty(){
		return theList.isEmpty();
	}
	
	public void displayQueue(){
		System.out.println("Queue (front-->rear)");
		theList.displayList();
	}
}

public class LinkQueue_demo {

	public static void main(String[] args) {
		// TODO 自动生成的方法存根
		LinkQueue theQueue = new LinkQueue();
		theQueue.push(10);
		theQueue.push(20);
		theQueue.push(30);
		theQueue.displayQueue();
		
		theQueue.pop();
		theQueue.pop();
		theQueue.displayQueue();
	}

}