鏈接列表中的數據不會顯示在GUI中的文本區域中。 Java的。爲什麼？

Question

我目前正在使用Java GUI在鏈接列表中執行圖書清單系統。我必須將書籍信息添加到鏈接列表中的節點，並通過實現迭代器來顯示它。

我已經完成了我的代碼，它顯示沒有錯誤。但是，當我運行GUI併成功將書籍添加到鏈接列表中時，請按下顯示按鈕。它沒有顯示我剛添加到文本區域的信息。

我的代碼的任何地方有問題嗎？

這是我的Node類：

public class Node 
{ 
    Data data; 
    Node next; 

    public Node() 
    { 
     next = null; 
    } 

    Node(Data data, Node next) 
    { 
     this.data = data; 
     this.next = next; 
    } 

    public Object getData() 
    { 
     return data; 
    } 

    public Node getNext() 
    { 
     return next; 
    } 

    public void setNext(Node next) 
    { 
     this.next=next; 
    } 
} 

這是我的LinkedList類與插入和顯示方法：

public class LinkedList 
{ 
    Node node = new Node(); 
    static Data data; 
    static Node head; 

    public LinkedList() 
    { 
     head=null; 
    } 

    public Node getHead() 
    { 
     return head; 
    } 

    public static void addNode(Data data) 
    { 
     Node newNode = new Node(data, head); 
     Node previous = null; 
     Node current = head; 

     while(current != null && data.name.compareTo(current.data.name) >= 0){ 
      previous = current; 
      current = current.next; 
     } 

     if(previous == null){ 
      head = newNode; 
     }else{ 
      previous.next = newNode; 
     } 
      newNode.next = null; 
      JOptionPane.showMessageDialog(null,"Book Information has been added to the inventory."); 
    } 
} 

    public static String displayNode() 
    { 
     DisplayIterator i; 
     Node current = head; 
     String output = "";  
     while(DisplayIterator.hasNext()) 
     { 
      output+= DisplayIterator.next(); 
      current=current.next; 
     }  
     return output+"NULL"; 
    } 

這是我用於存儲所有的信息我的數據類到一個節點：

public class Data { 
    String name; 
    String author; 
    int isbn; 
    int number; 
    String genre; 
    Node head; 

    public Data(String name, String author, int isbn, int number, String genre) 
    { 
     this.name = name; 
     this.author = author; 
     this.isbn = isbn; 
     this.number = number; 
     this.genre = genre; 
    } 

    public String toString(String name, String author, int isbn, int number, String genre) 
    { 
     return("Book Name: "+name+"\nAuthor: "+author+"\nISBN Number: "+isbn+"\nNumber of Copies: "+number+"\nGenre: "+genre+"\n"); 
    } 
} 

最後這是我的迭代類：

public class DisplayIterator 
{ 
    Data data; 
    static Node current; 

    DisplayIterator(Data data) 
    {  
     this.data = data; 
     current = data.head;  
    } 

    public static boolean hasNext() 
    { 
     if(current != null){    
      return true; 
     }  
     return false;  
    } 

    public static Object next() 
    { 
     if(hasNext()){ 
     current = current.getNext(); 
     return current.getData().toString();    
    }  
     return null;   
    } 

    public void remove() 
    { 
     throw new UnsupportedOperationException("It is read-only.");   
    }  
} 

我認爲問題出在DisplayIterator類上，但我看不到在哪裏。 任何人都可以幫助我嗎？謝謝。

Answer 1

你data.head總是空

DisplayIterator(Data data) 
{  
    this.data = data; 
    current = data.head; // this will always make current as null. 
} 

在你的下面的類，構造函數不初始化頭節點。

public class Data { 
    String name; 
    String author; 
    int isbn; 
    int number; 
    String genre; 
    Node head; // not set any where? 

此外，您的addNode不正確。

public static void addNode(Data data) 
{ 
    Node newNode = new Node(data, head); 
    Node previous = null; 
    Node current = head; //this will be always NULL on first addNode call 

    while(current != null && data.name.compareTo(current.data.name) >= 0){ 
     previous = current; 
     current = current.next; 
    } 

    if(previous == null){ 
     head = newNode; 
    }else{ 
     previous.next = newNode; 
    } 
     newNode.next = current; // how can be newNode.next is current? 
     JOptionPane.showMessageDialog(null,"Book Information has been added to the inventory."); 
}