我应该期待一个循环链表队列向后打印吗？

Question

我想实现一个单引用的循环链表队列。我相信这是基于测试的先进先出（每次元素入队后都会更新），但是它是反向打印的。我应该期待这一点，还是我错过了一些东西？我试过改变toString（）。这里是我CircularLinkedQueue类：

public class CircularLinkedQueue implements UnboundedQueueInterface 

{ 

protected LLObjectNode rear;   

public CircularLinkedQueue() 
{ 
    rear = null; 
} 


public void enqueue(Object element) 
{ 
    LLObjectNode newNode = new LLObjectNode(element); 

    if (rear == null) 
     newNode.setLink(newNode); 

    newNode.setLink(rear);  
    rear = newNode;  
}// end enqueue() 


public Object dequeue() throws QueueUnderflowException 
{ 
    if (isEmpty()) 
     throw new QueueUnderflowException("Dequeue attempted on an empty queue."); 
    else 
    { 
     Object element;     // create a reference to the Object to return 
     element = rear.getLink();  // set the reference to the information in the front node 
     rear = rear.getLink();   // set the rear reference to point at the next node 

     return element;     
    }// end else 
}// end dequeue() 


public boolean isEmpty() 
{ 
    return (rear == null);    
}// end isEmpty() 


// *** Exercise #25b  *** works 
public Object front() 
// returns a reference to the front element on the queue. 
// precondition: queue is not empty. 
{ 
    Object frontObj; 
    frontObj = rear.getLink(); 
    return frontObj; 
}// end front() 


public int size() 
{ 
    LLObjectNode node; 
    node = rear; 
    int count = 0; 

    while (node != null) 
    { 
     count++; 
     node = node.getLink(); 
    } 
    return count; 
}// end size() 


public String toString() 
{ 
    String circleQStr = ""; 
    LLObjectNode node; 
    int count = 0; 
    node = rear; 

    while (node != null) 
    { 
     count++; 
     circleQStr = circleQStr + count + ". " + node.getInfo() + "\n"; 
     node = node.getLink(); 
    }// end while 
    return circleQStr; 
    }// end toString() 
}// end class CircularLinkedQueue 

这里是getLink()和setLink()：

public void setLink(LLObjectNode link) 
{ 
    // sets link of this LLObjectNode 
    this.link = link; 
} 


public LLObjectNode getLink() 
{ 
    // returns link of this LLObjectNode 
    return link; 
} 

感谢您阅读我的文章。

Answer 1

这个代码存在很多问题，我认为这与您声明的问题无关，但如果您的起始节点位于后方，那么您需要在打印之前先行前进，否则它将首先打印后方。另外...我不认为你的size()函数将永远返回...在循环队列中，下一个元素永远不会为空。这也是很难调试这没有你发布的getLink()和代码setLink()

编辑好吧，我认为问题是，你的enequeue方法应该是这样的

public void enqueue(Object element) 
{ 
    LLObjectNode newNode = new LLObjectNode(element); 

    if (rear == null){ 
     newNode.setLink(newNode); 

    }else{ 
     newNode.setLink(rear.getLink()); 
     rear.setLink(newNode);  
    } 

    rear = newNode; 
}// end enqueue() 

此外，你需要改变你的出队方法。现在你的后方指向刚刚出队的元素。

public Object dequeue() throws QueueUnderflowException 
{ 
    if (isEmpty()) 
     throw new QueueUnderflowException("Dequeue attempted on an empty queue."); 
    else 
    { 
     Object element;     // create a reference to the Object to return 
     element = rear.getLink();  // set the reference to the information in the front node 
     rear.setLink(element.getLink());   // set the rear reference to point at the next node 

     return element;     
    }// end else 
}// end dequeue()