I am learning binary trees in Java using Eclipse, and I want to traverse a binary tree in preorder, but I am not sure if my implementation is correct.

class Node {

    int data;
    Node left;
    Node right;

    public Node(int data) {
        this.data = data;
        left = null;
        right = null;
    }
}

public class Main {

    public static void preorder(Node root) {

        if (root != null) {

            System.out.println(root.data);

            preorder(root.left);

            preorder(root.right);
        }
    }

    public static void main(String[] args) {

        Node root = new Node(10);

        root.left = new Node(5);
        root.right = new Node(20);

        root.left.left = new Node(3);

        preorder(root);
    }
}

I want to confirm whether this output actually corresponds to a preorder traversal.

What I Have Tried

• I compared the output with examples online.

• I reviewed the order of the recursive calls.

• I changed the print order and got different results.