java - 访问 ArrayList 中的引用时出现问题

Question

无法将新元素(节点)添加到ArrayList

Node N = new Node(5,"Sandeep");
Node N1 = new Node(5,"qwert");

在下面的行中，我收到空指针异常

N.children.add(N1)

代码:

class Node {
    public int val;
    public String data;
    public ArrayList<Node> children;

    public Node(int val, String data) {
        this.val = val;
        this.data = data;
        ArrayList<Node> children = new ArrayList<Node>();
    }
}

public class Nary {
    public static void main(String[] args) {            
       // ArrayList<Node> children = new ArrayList<Node>();
        Node N = new Node(5,"Sandeep");
        Node N1 = new Node(5,"qwert");
        N.children.add(N1);
    }
}

Answer 1

在代码中更改此内容

class Node {

    public int val;
    public String data;
    public ArrayList<Node> children;

    public Node(int val, String data) {
        this.val = val;
        this.data = data;
        this.children = new ArrayList<Node>();
    }

}