All elements in arrayList is null when add to arrayList in java

Question

I have created a List call nodes_ and initialized as a ArrayList, when I add something to nodes_ , all is null. There is a piece of code :

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);

and there is another piece of other class:

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);
}

When i debuged , it looks like this : debug image

Answer 1

What you're seeing ( "null" ) is the output of toString() called on each of those classes. They aren't actually null.

How can you tell? The debugger shows each entry like ClassNode@464 . That refers to a specific instance, not null.

Answer 2

The nodes are not null. The objects are all there, but their toString representation is "null".