inserting in binary tree doesn't work using java

Question

I\'m currently learning about trees using java and i have some errors going on here in the insertion of items in a binary tree I don\'t why it doesn\'t work

this is the

Answer 1

root is always null because you never assign value to it.

you can add to the beginning of your method check and assign it

public TNode insertNode(TNode item, int d){
    if(item == null){
        TNode node = new TNode(d);
        if (root == null) { 
            root = node;
        }
        return node
    }
    ... rest of method isn't changed...

Also when you are recursing you should make a call with a proper child node instead of always calling with item, so for example first case would be:

    item.left = insertNode(item.left, d);

For second case you would just use item.right instead.

Answer 2

Fine code, but recursing does not step further

item.left = insertNode(item.left, d);
item.right = insertNode(item.right, d);

And the initial root is not updated:

root = insertNode(root, d);

The else part or final return is superfluous.

---

Something on the code style

insertNode has a node as input, and returns the updated node value, hence the call "pattern" should look like

X = insertNode(X, d); // X is some expression

This is because java can never assign to the passed argument expression: it has no pass-by-reference, but pass-by-value; f(x) never assigns to x.