java - 绘制节点的图片以及它们指向的位置

Question

我应该直观地解释在输入以下代码后四个节点是如何出现的:

public class Node
{

    //These two lines are provided
    public Object Data = null;
    public Node Next = null;

    public static void main(String[] args)
    {
        Node a = new Node();
        Node b = new Node();
        Node c = new Node();
        Node d = new Node();

        //These four lines must be used
        b = a.Next;
        //c = b.Next;                //Gives NullPointer error
        //b.Data = c.Next.Data;      //Gives NullPointer error
        c.Next = a;
    }
}

从我迄今为止所做的工作来看，似乎:

• A 指向一个 Node(不变)
• B 变成空对象
• C的节点指向A
• D 指向一个 Node(不变)

( 这是我从调试器中引用的图像)

上面两行给出NullPointer错误正常吗？我的猜测和图片有点接近吗？感谢您的帮助

Answer 1

鉴于每个 Node 对象的 Data 和 Next 为空，让我们从您的主功能。 (建议您使用驼峰命名法来命名这些变量 https://en.wikipedia.org/wiki/Camel_case )

Node A = new Node(); 
Node B = new Node(); 
Node C = new Node(); 
Node D = new Node(); // Defines non-null A, B, C, and D Nodes

B = A.Next; // B = null; because the Next and Data of each node is null

C = B.Next; // C = (a non existent) b.next causing a null pointer error
B.Data = C.Next.Data; // c.next == null. null.Data doesn't exist. 

C.Next = A; // C.Next = A; A == new Node(); no error