If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.This is 4th part of java binary tree tutorial.
In this post, we will see about InOrder binary tree traversal in java.
InOrder traversal:
In InOrder traversal,each node is processed between subtrees.In
simpler words,Visit left subtree, node and then right subtree.
Steps for InOrder traversal are:
 Traverse the left subtree in InOrder.
 Visit the node.
 Traverse the right subtree in InOrder.
 Recursive
 Iterative
Recursive solution is very straight forward.Below diagram will make you understand recursion better.
Code for recursion will be:
public void inOrder(TreeNode root) { if(root != null) { inOrder(root.left); //Visit the node by Printing the node data System.out.printf("%d ",root.data); inOrder(root.right); } }Iterative solution:
For recursion, we use implicit stack. So here to convert recursive solution to iterative, we will use explicit stack.
Steps for iterative solution:
 Create an empty stack s and Initialize current node as root
 Push the current node to s and set currentNode = currentNode.left until currentNode is NULL
 If currentNode is NULL and s is not empty then
 Pop the top node from stack and print it
 set currentNode = currentNode.right
 go to step 2
 If stack is empty and currentNode is also null then we are done with it
public void inOrderIter(TreeNode root) { if(root == null) return; Stack<TreeNode> s = new Stack<TreeNode>(); TreeNode currentNode=root; while(!s.empty()  currentNode!=null){ if(currentNode!=null) { s.push(currentNode); currentNode=currentNode.left; } else { TreeNode n=s.pop(); System.out.printf("%d ",n.data); currentNode=n.right; } } }
Lets create java program for InOrder traversal:
package org.arpit.java2blog; import java.util.Stack; public class BinaryTree { public static class TreeNode { int data; TreeNode left; TreeNode right; TreeNode(int data) { this.data=data; } } // Recursive Solution public void inOrder(TreeNode root) { if(root != null) { inOrder(root.left); //Visit the node by Printing the node data System.out.printf("%d ",root.data); inOrder(root.right); } } // Iterative solution public void inOrderIter(TreeNode root) { if(root == null) return; Stack<TreeNode> s = new Stack<TreeNode>(); TreeNode currentNode=root; while(!s.empty()  currentNode!=null){ if(currentNode!=null) { s.push(currentNode); currentNode=currentNode.left; } else { TreeNode n=s.pop(); System.out.printf("%d ",n.data); currentNode=n.right; } } } public static void main(String[] args) { BinaryTree bi=new BinaryTree(); // Creating a binary tree TreeNode rootNode=createBinaryTree(); System.out.println("Using Recursive solution:"); bi.inOrder(rootNode); System.out.println(); System.out.println(""); System.out.println("Using Iterative solution:"); bi.inOrderIter(rootNode); } public static TreeNode createBinaryTree() { TreeNode rootNode =new TreeNode(40); TreeNode node20=new TreeNode(20); TreeNode node10=new TreeNode(10); TreeNode node30=new TreeNode(30); TreeNode node60=new TreeNode(60); TreeNode node50=new TreeNode(50); TreeNode node70=new TreeNode(70); rootNode.left=node20; rootNode.right=node60; node20.left=node10; node20.right=node30; node60.left=node50; node60.right=node70; return rootNode; } }Run above program and you will get following output:
Using Recursive solution: 10 20 30 40 50 60 70  Using Iterative solution: 10 20 30 40 50 60 70
Java Binary tree tutorial:

Binary tree in java
Binary tree preorder traversal
Binary tree postorder traversal
Binary tree inorder traversal
Binary tree level order traversal
Binary tree spiral order traversal
Binary tree reverse level order traversal
Binary tree boundary traversal
Print leaf nodes of binary tree
Count leaf nodes in binary tree
get maximum element in binary tree
Print all paths from root to leaf in binary tree
Print vertical sum of binary tree in java
Get level of node in binary tree in java
Lowest common ancestor(LCA) in binary tree in java
Please go through java interview programs for more such programs.