数据结构——使用双端链表实现队列（java实现）

     队列是这样一种数据结构：在队尾（rear）插入数据项，在队首（front）移除数据项，队列的进出顺序是先进入的先被移除（先进先出，FIFO）；

     Robert Lafore的书对队列的使用有如下描述：“它可以用于模拟真实世界的环境，例如模拟人们在银行里排队等待，飞机等待起飞，或者因特网上数据包等待传送。在计算机（或网络）操作系统里，有各种队列在安静地工作着。打印作业在打印队列中等待打印。当在键盘上敲击时，也有一个存储键入内容的队列。同样，如果使用文字处理程序敲击一个键，而计算机又暂时要做其他的事，敲击的内容不会丢失，它会排在队列中等待，知道文字处理程序有时间来读取它。利用队列保证了键入内容在处理时其顺序不会改变。”

实现代码如下：

/*
*Imagine a queue in front of you,your left side is the front of the queue,your right side is the rear of queue;
*this seems more logical and close to real life
*
*/
class Link
{
public long dData;
public Link next;
public Link(long dData)
{
this.dData = dData;
}
public void displayLink()
{
System.out.print("{" + this.dData + "}");
}
}

class FirstLastList
{
Link first;
Link last;

public FirstLastList()
{
this.first = null; //when create an object of LinkList,make sure it is empty!
this.last = null;
}

public boolean isEmpty()
{
return first == null;
}

public void insertLast(long key) //this method will be used when I create insert() method
{ //in Queue(not the class Queue,I just mean a Queue)
Link newLink = new Link(key);
if(this.isEmpty()) //if list is empty
{
first = newLink; //draw a picture can help me understand it !
last = newLink;
newLink.next = null;
}
else
{
last.next = newLink;
last = newLink;
newLink.next = null;
}
}

public long deleteFirst() //this method will be used when I create remove() method in Queue(not the class Queue,I just mean a Queue)
{
Link current = null;
if(this.isEmpty())
{
System.out.println("Your stack is empty");
return -1;
}
else if(first==last)
{
current = first;
first = null;
last = null;
return current.dData;
}
else
{
current = first;
first = first.next;
return current.dData;
}

}

public void displayList()
{
Link current = first;
System.out.print("Queue (front-->rear): ");
if(this.isEmpty())
{
System.out.println("Your list is empty, nothing to show!");
}
else
{
while(current!=null)
{
current.displayLink();
current = current.next;
}
System.out.println("");
}
}
}

class LinkQueue
{
FirstLastList list = new FirstLastList(); //two-ended list
public void insert(long key)
{
list.insertLast(key);
}
public long remove()
{
return list.deleteFirst();
}
public void showQueue()

c0b4
{
list.displayList();
}
}

class LinkQueueApp
{
public static void main(String[] args)
{
LinkQueue theQueue = new LinkQueue();
theQueue.insert(12); //insert four elements
theQueue.insert(13);
theQueue.insert(14);
theQueue.insert(15);

theQueue.showQueue(); //look at what is in the queue

theQueue.remove(); //remove two elements ,from right side
theQueue.remove();
theQueue.showQueue(); //look at what is in the queue now!
}
}

代码的思路：首先创建一个新队列，接着在队列中一次插入12、13、14、15，在队列头部进行两次移除操作，最后运行结果如下：