一个更简单的方法是引入一个尾部和一个头部，使您的队列成为双端的，无需每次添加一个项时遍历整个队列。

class Queue {
       private Link head;
       private Link tail;

       public void insert(Object item) {
          Link add = new Link();
          add.data = item;
          add.next = null;

          if(head == null)
          {
             head = add;
             tail = add;
          }
          else {
             tail.next = add;
             tail = add;
          }
       }
}

确实应该调用该方法 add 因为它是附加到结尾而不是插入。

在代码中修复（改为字符串方法printlist）：

public class QuestionFive
    {
       public static void main(String[] args)
       {
          // creating a queue
          Queue q = new Queue();

          // adding numbers 1,2,3 and 4
          q.insert(1);
          q.insert(2);
          q.insert(3);
          q.insert(4);
          q.printList();
          System.out.println(q);
       }
    }
    class Queue 
    {
       //Private Data Member
       private Link _head;

       //Constructor: A constructor to create an empty Queue,
       public Queue() 
       {
          _head = null;
       }

       //Insert Method: A method to insert a given Object into the Queue.
       //Note: We will inserton
       public void insert(Object item) 
       {
          Link add = new Link();
          add.data = item;
          add.next = _head;
          _head = add;

       }

       //Prints list data
       public void printList() {
           Link currentLink = _head;
           System.out.print("List: ");
           while(currentLink != null) {
               currentLink.printLink();
               currentLink = currentLink.next;
           }
           System.out.println("");
       }

       //Delete Method: A method to delete an Object from the Queue
       public Object delete() 
       {
            if ( _head == null ) return null; 

            Link prev = null;    
            Link curr = _head;     
            while (curr.next != null )    
            {      
                prev = curr;      
                curr = curr.next; 
            }     
            if ( prev != null ) 
            {
                prev.next = null; 
            }   
            else
            {       
                _head = null;   
            } 
            return curr.data;
        }

        // IsEmpty Method: A method to test for an empty Queue
        public boolean isEmpty() 
        {
          // queue is empty if front is null
          return (_head == null);
        }

    }

    //Link Class
    class Link 
    {
       public Object data;
       public Link next;
       //Print Link data
       public void printLink() {
           System.out.print("{" + data + "}");
       }
    }

你的逻辑 insert() 方法需要注意。我已经修改了 else 该方法的一部分如下所示，并且起到了作用：

else
          {
             for(Link curr = _head; ; curr = curr.next)
             {
                if(curr.next == null){
                    curr.next = add;
                    break;
                }
             }
          }

以下是全体工人阶级：

public class QuestionFive
    {
       public static void main(String[] args)
       {
          // creating a queue
          Queue q = new Queue();

          // adding numbers 1,2,3 and 4
          q.insert(1);
          q.insert(2);
          q.insert(3);
          q.insert(4);

          System.out.println(q);
       }
    }
    class Queue 
    {
       //Private Data Member
       private Link _head;

       //Constructor: A constructor to create an empty Queue,
       public Queue() 
       {
          _head = null;
       }

       //Insert Method: A method to insert a given Object into the Queue.
       //Note: We will inserton
       public void insert(Object item) 
       {
          Link add = new Link();
          add.data = item;
          add.next = null;

          if(_head == null)
          {
             _head = add;
          }
          else
          {
             for(Link curr = _head; ; curr = curr.next)
             {
                if(curr.next == null){
                    curr.next = add;
                    break;
                }
             }
          }
       }

       //Delete Method: A method to delete an Object from the Queue
       public Object delete() 
       {
            if ( _head == null ) return null; 

            Link prev = null;    
            Link curr = _head;     
            while (curr.next != null )    
            {      
                prev = curr;      
                curr = curr.next; 
            }     
            if ( prev != null ) 
            {
                prev.next = null; 
            }   
            else
            {       
                _head = null;   
            } 
            return curr.data;
        }

        // IsEmpty Method: A method to test for an empty Queue
        public boolean isEmpty() 
        {
          // queue is empty if front is null
          return (_head == null);
        }

        //toString Method:
        public String toString()
        {
          String s = "";
          for (Link curr = _head; curr != null; curr = curr.next)
          {
              s = s + " " + curr.data;
          }
          return s;
        }
    }

    //Link Class
    class Link 
    {
       public Object data;
       public Link next;
    }