BinaryTree implementation: something wrong with the inorder traversal?

Your problem is in public void createNodes(Node temp, T data) function. You pass in a parameter the same name as the class variable temp. First of all I don't think you need the class variable by itself. Second of all assigning to temp in this method has only local effect - you loose the information in the temp parameter, but setting temp, will not infuence its value in the called method. I suggest you rewrite the method so that it returns the pointer to the newly created node and assign this pointer to the left and right of the local temp. That way the changes will propagate out.

Best way to implement Binary Tree in Java with all the traverse types and test cases as below

package com.nitin.tree; public class Tree { private Node parent; private int data; private int size = 0; public Tree() { parent = new Node(data); } public void add(int data) { if (size == 0) { parent.data = data; size++; } else { add(parent, new Node(data)); } } private void add(Node root, Node newNode) { if (root == null) { return; } if (newNode.data < root.data) { if (root.left == null) { root.left = newNode; size++; } else { add(root.left, newNode); } } else { if (root.right == null) { root.right = newNode; size++; } else { add(root.right, newNode); } } } public int getLow() { Node current = parent; while (current.left != null) { current = current.left; } return current.data; } public int getHigh() { Node current = parent; while (current.right != null) { current = current.right; } return current.data; } private void in(Node node) { if (node != null) { in(node.left); System.out.print(node.data + " "); in(node.right); } } private void pre(Node node) { if (node != null) { System.out.print(node.data + " "); pre(node.left); pre(node.right); } } private void post(Node node) { if (node != null) { post(node.left); post(node.right); System.out.print(node.data + " "); } } public void preorder() { System.out.print("Preorder Traversal->"); pre(parent); System.out.println(); } public void postorder() { System.out.print("Postorder Traversal->"); post(parent); System.out.println(); } public void inorder() { System.out.print("Inorder Traversal->"); in(parent); System.out.println(); } private class Node { Node left; Node right; int data; public Node(int data) { this.data = data; } } public String toString() { Node current = parent; System.out.print("Traverse From Left "); while (current.left != null && current.right != null) { System.out.print(current.data + "->[" + current.left.data + " " + current.right.data + "] "); current = current.left; } System.out.println(); System.out.print("Traverse From Right "); current = parent; while (current.left != null && current.right != null) { System.out.print(current.data + "->[" + current.left.data + " " + current.right.data + "] "); current = current.right; } return ""; } public static void main(String af[]) { Tree t = new Tree(); t.add(40); t.add(25); t.add(78); t.add(10); t.add(32); t.add(50); t.add(93); t.add(3); t.add(17); t.add(30); t.add(38); System.out.println(t.getLow()); System.out.println(t.getHigh()); System.out.println("Size-" + t.size); System.out.println(t); t.inorder(); t.preorder(); t.postorder(); } } 

another type of outputting the tree:

public void inorder() { inorder(root); } protected void visit(BSTNode<T> p) { System.out.println("Node: " + p.el + "Left Side:" + (p.left!=null?p.left.el:"null") + "Right Side:" + (p.right!=null?p.right.el:"null")); } 

I've changed the BinaryTree Class as below. See the change on the the createNode method in particular.

The problem, as mentioned in the post before this, is that your reference doesn't persist when it is passed as an argument to the createNode method. That change is only local. You need to return an explicit Node reference in the method itself as you're creating the node.

public Node createNode() { Integer value = getData(); Node temp = new Node(value); if(head==null) { head = temp; } System.out.println("Do you want to add left branch on node("+value+")? Enter y/n"); if(input.next().charAt(0)=='y') { temp.left=createNode(); } System.out.println("Do you want to add right branch on node("+value+")? Enter y/n"); if(input.next().charAt(0)=='y') { temp.right=createNode(); } return temp; } 

Here is the resulting output:

 Basic operations on a tree: 1. Create tree 2. Insert 3. Search value 4. print list Else. Exit Choice:1 Basic operations on a tree: 1. Create tree 2. Insert 3. Search value 4. print list Else. Exit Choice:2 Enter the value to insert: 10 Do you want to add left branch on node(10)? Enter y/n y Enter the value to insert: 20 Do you want to add left branch on node(20)? Enter y/n n Do you want to add right branch on node(20)? Enter y/n n Do you want to add right branch on node(10)? Enter y/n y Enter the value to insert: 30 Do you want to add left branch on node(30)? Enter y/n n Do you want to add right branch on node(30)? Enter y/n n Basic operations on a tree: 1. Create tree 2. Insert 3. Search value 4. print list Else. Exit Choice:4 20 10 30 

I hope this will be of some help to someone later (even if this is 3 years late..). I just started learning about Binary Trees today myself. I'm actually planning on using this as a base to doing more involved tasks!

I changed the createNode method so that it works:

public Node createNode(Node temp, Integer value) { Node newnode = new Node(); value = getData(); newnode.data = value; temp = newnode; if(head == null) { head = temp; } System.out.println("If left child exits for ("+value+") enter y else n"); if(input.next().charAt(0) == 'y') { newnode.left = createNode(newnode.left, value); } System.out.println("If right child exits for ("+value+") enter y else n"); if(input.next().charAt(0) == 'y') { newnode.right = createNode(newnode.right, value); } return newnode; }