访问 ArrayList 中的引用时出现问题

Question

无法添加新元素（节点）到ArrayListNode 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

在您的代码中更改此设置

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>();

    }

}

Answer 2

在 Node 构造函数中，您正在创建 Children 的新本地属性如果您在构造函数中进行以下更改，它将正常工作 this.children = new ArrayList();