java - java中添加到arrayList时，arrayList中的所有元素均为null

Question

我创建了一个List调用nodes_并初始化为ArrayList，当我向nodes_添加一些东西时，一切都是空的。有一段代码:

public class MyOocmdgGeneration1 {
private List<Node> nodes_ = new ArrayList<Node>();

public MyOocmdgGeneration1() {
    findDependency();
}

private void findDependency() {

    ClassNode c1 = new ClassNode();
    FieldNode x = new FieldNode();
    MethodNode c1Constructor = new MethodNode();
    MethodNode m1 = new MethodNode();

    nodes_.add(c1);
    nodes_.add(x);
    nodes_.add(c1Constructor);
    nodes_.add(m1);

还有另外一个类:

public abstract class Node {
private String path;
private List<Node> callees;
private List<Node> callers;
private List<Node> children;
private Node parent;
private int id;

public Node() {
    this.callees = new ArrayList<>();
    this.callers = new ArrayList<>();
    this.children = new ArrayList<>();
}

public Node(String path, List<Node> callees, List<Node> callers) {
    this();
    this.path = path;
    this.callees = callees;
    this.callers = callers;
    this.children = new ArrayList<>();
}

public Node(int id, String path, Node parent) {
    this();
    this.id = id;
    this.path = path;
    this.parent = parent;
    parent.addChild(this);
}

当我调试时，它看起来像这样:debug image

Answer 1

您所看到的 ("null") 是在每个类上调用的 toString() 的输出。它们实际上并不为空。

你怎么知道？调试器显示每个条目，如 ClassNode@464。它指的是一个特定的实例，不为空。