队列实现中的出队和入队方法

Question

我在读java队列中的队列。我发现下面的代码

public class QueueOfStrings { 

    private Node first = null; // least-recently added 
    private Node last = null; // most-recently added 

    private class Node { 

     private String item; 
     private Node next; 
    } 

    // is the queue empty? 
    public boolean isEmpty() { 
     return first == null; 
    } 

    public String dequeue() { 
     if (isEmpty()) { 
      throw new RuntimeException("Queue underflow"); 
     } 
     String item = first.item; 
     first = first.next; 
     return item; 
    } 

    public void enqueue(String item) { 
     Node x = new Node(); 
     x.item = item; 
     if (isEmpty()) { 
      first = x; 
      last = x; 
     } else { 
      last.next = x; 
      last = x; 
     } 
    } 

我没有改写他们在我的方式是这样的：

public String dequeue() { 
    if (isEmpty()) { 
     throw new RuntimeException("Queue underflow"); 
    } else if (first = last) { 
     String f = first.item; 
     first = null; 
     last = null; 
     return f; 
    } 

    String f = first.item; 
    first = first.next; 
    return f; 

} 
public void enqueue(String item) { 
    Node x = new Node(item); 
    if (first = last = null) { 
     first = last = x; 
    } 
    last.next = x; 
    last = x; 
} 

我在出队右做（）和排队（）方法？

在main方法，我应该这样做：

public static void main(String[] args) { 

    QueueOfStrings q = new QueueOfStrings(); 
    q.enqueue("roro"); 
    q.enqueue("didi"); 
    q.enqueue("lala"); 

    System.out.println(q.dequeue()); 
} 

感谢

Answer 1

public String dequeue() { 
    if (isEmpty()) { 
     throw new RuntimeException("Queue underflow"); 
    } else if (first == last) { 
     String f = first.item; 
     first = null; 
     last = null; 
     return f; 
    } 

    String f = first.item; 
    first = first.next; 
    return f; 

} 
public void enqueue(String item) { 
    Node x = new Node(item); 
    if (first == null && last == null) { 
     first = x; 
     last = x; 
     return; // return back when first node is enqueued 
    } 
    last.next = x; 
    last = x; 
}