Question

Why does this line of code in my Tree class not work. I get an error on the add(child).

    public void addChild(TreeNode<T> parent, TreeNode<T> child)
{
    parent.children.add(child);
}

Here is TreeNode

public class TreeNode<E> {

protected int accountNum;
protected ArrayList<E> children;

Answer 1

That’s because children is an ArrayList of E, not of TreeNode<E>, while child is a TreeNode<E>.

Depends on your needs, it could be either:

public void addChild(TreeNode<T> parent, T child)

Or:

protected ArrayList<TreeNode<E>> children;