堆棧推送方法無限循環Java

Question

我不明白爲什麼printList（）在調用時無限循環。我試圖編寫一個堆棧鏈表並打印列表，而不使用java中的內置堆棧方法。爲什麼我的打印方法無限循環，我該如何糾正這個問題？

public class LinkedListStack{ 
    private String item; 
    private Node next; 
    private Node top = null; 

    public LinkedListStack(){ 
    } 

    public void push(String item){ 
     top = new Node(item, top); 
    } 

    public void printList(){ 
     Node currentNode = top; 
     for(currentNode = top; currentNode.getItem()!= null; currentNode = currentNode.getNext()){ 
      System.out.println(currentNode.getItem()); 
     } 
    } 

    public class Node{ 
     public Node(String newItem, Node nextNode){ 
      item = newItem; 
      next = nextNode; 
     } 

     public Node(String newItem){ 
      item = newItem; 
      next = null; 
     } 

     //to set the value of the next field 
     public void setNext(Node nextNode){ 
      next = nextNode; 
     } 

     //read the value of the next field 
     public Node getNext(){ 
      return(next); 
     } 

     //to set the value of the item field 
     public String setItem(String newItem){ 
      item = newItem; 
      return(item); 
     } 

     //read the value of the item field 
     public String getItem(){ 
      return(item); 
     } 
    } 

    public static void main(String args[]){ 
     LinkedListStack newList = new LinkedListStack(); 
     newList.push("hello"); 
     newList.push("goodbye"); 
     newList.printList(); 
    } 
} 

Answer 1

問題是item和next是LinkedListStack領域和所有Node實例之間共享。當您創建另一個Node並設置該項目時，您將更改全部節點。要解決它，只需將字段聲明移至Node內部類。 除此之外，printList方法中的循環條件是錯誤的：下一個節點爲空，而不是其項目。 這裏是一個工作示例：

public class LinkedListStack { 
    private Node top = null; 

    public LinkedListStack() { 
    } 

    public void push(final String item) { 
     top = new Node(item, top); 
    } 

    public void printList() { 
     Node currentNode = top; 
     for (currentNode = top; currentNode != null; currentNode = currentNode.getNext()) { 
      System.out.println(currentNode.getItem()); 
     } 
    } 

    public class Node { 
     private String item; 
     private Node next; 

     public Node(final String newItem, final Node nextNode) { 
      item = newItem; 
      next = nextNode; 
     } 

     public Node(final String newItem) { 
      item = newItem; 
      next = null; 
     } 

     // to set the value of the next field 
     public void setNext(final Node nextNode) { 
      next = nextNode; 
     } 

     // read the value of the next field 
     public Node getNext() { 
      return next; 
     } 

     // to set the value of the item field 
     public String setItem(final String newItem) { 
      item = newItem; 
      return item; 
     } 

     // read the value of the item field 
     public String getItem() { 
      return item; 
     } 
    } 

    public static void main(final String args[]) { 
     final LinkedListStack newList = new LinkedListStack(); 
     newList.push("hello"); 
     newList.push("goodbye"); 
     newList.printList(); 
    } 
}