This tutorial provides code for implementing in-order traversal of a Binary Tree.

In-Order Traversal of Binary Tree

Binary Tree traversal is a process of visiting each node of Binary Tree exactly once. In-Order traversal falls into depth-first search as search is deepended on child nodes of a node before moving to its sibling.

In-order traversal is a special type of Tree traversal wherein left node data is printed before node data followed by right child node data. This results into recursive function calls as you can't print a node unless all of its left node data has been printed.

Let's consider below Binary Tree - 

Here is the In-Order Traversal of above tree -

10 20 30 40 50 60 70 80 90 

Java Implementation of In-Order Traversal of Binary Tree

Here is Java code for Binary Tree containing methods for inserting data and in-order traversal - 

package com.aksain.data.structures;

public class BinaryTreeWithInOrderTraversal<T extends Comparable<T>> {
	private Node root;
	
	private class Node {
		T data;
		Node left;
		Node right;
		
		private Node(T data) {
			this.data = data;
		}
	}
	
	private Node doInsert(T data, Node node) {
		if(node == null) {
			return new Node(data);
		}
		int result = data.compareTo(node.data);
		if(result < 0) {
			node.left = doInsert(data, node.left);
		} else if(result > 0) {
			node.right = doInsert(data, node.right);
		}
		
		return node;
	}
	
	public void insert(T data) {		
		root = doInsert(data, root);
	}
	
	private void doInOrder(Node node) {
		if(node == null) {
			return;
		}
		doInOrder(node.left);
		System.out.print(node.data + " ");
		doInOrder(node.right);
	}
	
	public void inOrder() {
		doInOrder(root);
		System.out.println();
	}
	
	public static void main(String[] args) {
		final BinaryTreeWithInOrderTraversal<Integer> binaryTree = new BinaryTreeWithInOrderTraversal<>();
		binaryTree.insert(50);
		binaryTree.insert(30);
		binaryTree.insert(10);
		binaryTree.insert(20);
		binaryTree.insert(40);
		binaryTree.insert(70);
		binaryTree.insert(60);
		binaryTree.insert(80);
		binaryTree.insert(90);
		
		binaryTree.inOrder();
	}
}

Here is the output of above code - 

10 20 30 40 50 60 70 80 90 

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