public class BinaryTree {
    TreeNode root;

    public void inOrder() {
        inOrder(root);
    }

    private void inOrder(TreeNode node) {
        inOrder(node.left);
        System.out.println(node.data);
        inOrder(node.right);
    }

    public void preOrder() {
        preOrder(root);
    }

    private void preOrder(TreeNode node) {
        System.out.println(node.data);
        preOrder(node.left);
        preOrder(node.right);
    }

    public void postOrder() {
        postOrder(root);
    }

    private void postOrder(TreeNode node) {
        preOrder(node.left);
        preOrder(node.right);
        System.out.println(node.data);
    }

    public void levelOrder() {
        Queue<TreeNode> queue = new LinkedList();
        queue.add(root);
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            System.out.println(node);
            if (root.left != null) {
                queue.add(root.left);
            }
            if (root.right != null) {
                queue.add(root.right);
            }
        }
    }
}