LinkedList 空指针错误。当尝试打印 LinkedList 中的元素时，我不断收到空指针异常

Question

我在尝试打印列表中的元素时不断出现空指针异常。异常发生在 print() 中我开始 while 循环的行。有没有办法来解决这个问题？谢谢

class LinkedLists {

    private Node node;  

    public LinkedLists() {  
        
    }

    public void add(int d) {
        Node newNode = new Node(d);
        Node curr = node;
    
        if(curr == null) 
            curr = newNode;
    
    
        while(curr.next != null) {
            curr = curr.next;       
        }       
        curr.next = newNode;
    
        return;
    }

    public void print() {
    
        Node curr = node;
    
        while(curr.next != null) {
            System.out.println(curr.data);
            curr = curr.next;
        }
        System.out.println(curr.data);  
    }


    public static void main(String[] args) {
        LinkedLists list = new LinkedLists();
        list.add(3);
        list.add(12);
        list.add(99);
        list.add(6);
    
        list.print();       
    }

}

public class Node {

    Node next;
    int data;

    public Node(int d) {
        data = d;
        next = null;        
    }
}

Answer 1

尝试这样做

public class Node 
 {
  Node? next;
  int data;

  public Node(int d)
   {
    this.data = d;
    this.next = null;   
   }
 }

不用担心 this 关键字