Java Program to Perform the inorder tree traversal

In this article, we will understand how to perform the inorder tree traversal. In InOrder traversal, each node is processed between subtrees.In simpler words, visit left subtree, node and then right subtree.

Below is a demonstration of the same −

Suppose our input is −

Run the program

The desired output would be −

The In-Order traversal of the tree_object is:
5->12->6->1->9->

Algorithm

Step 1 - START
Step 2 - A class with the data specifications is previously defined.
Step 3 - Create a new instance of the class.
Step 4 - Initialize the instance with relevant values.
Step 5 - Invoke the method to perform inorder traversal.
Step 6 - Display the result
Step 7 - Stop

Example 1

Here, we have used the recursive method for in-order traversal.

class Node {
   int item;
   Node left_node, right_node;
   public Node(int key) {
      item = key;
      left_node = right_node = null;
   }
}
public class Tree {
   Node root;
   Tree() {
      root = null;
   }
   void inOrder(Node node) {
      if (node == null)
         return;
      inOrder(node.left_node);
      System.out.print(node.item + "->");
      inOrder(node.right_node);
   }
   public static void main(String[] args) {
      Tree tree_object = new Tree();
      System.out.println("A tree_object object is defined: ");
      tree_object.root = new Node(1);
      tree_object.root.left_node = new Node(12);
      tree_object.root.right_node = new Node(9);
      tree_object.root.left_node.left_node = new Node(5);
      tree_object.root.left_node.right_node = new Node(6);
      System.out.println("The In-Order traversal of the tree_object is: ");
      tree_object.inOrder(tree_object.root);
   }
}

Output

A tree_object object is defined:
The In-Order traversal of the tree_object is:
5->12->6->1->9->

Example 2

Here, we are using the non-recursive method for in-order traversal.

import java.util.Stack;
class Node {
   int data;
   Node left_node, right_node;
   public Node(int item) {
      data = item;
      left_node = right_node = null;
   }
}
public class tree {
   Node root;
   void inorder() {
      if (root == null)
         return;
      Stack<Node> temp_stack = new Stack<Node>();
      Node current_node = root;
      while (current_node != null || temp_stack.size() > 0) {
         while (current_node != null) {
            temp_stack.push(current_node);
            current_node = current_node.left_node;
         }
         current_node = temp_stack.pop();
         System.out.print(current_node.data + " ");
         current_node = current_node.right_node;
      }
   }
   public static void main(String args[]) {
      tree tree = new tree();
      System.out.println("A tree_object object is defined: ");
      tree.root = new Node(1);
      tree.root.left_node = new Node(2);
      tree.root.right_node = new Node(3);
      tree.root.left_node.left_node = new Node(4);
      tree.root.left_node.right_node = new Node(5);
      System.out.println("The In-Order traversal of the tree_object is: ");
      tree.inorder();
   }
}

Output

A tree_object object is defined:
The In-Order traversal of the tree_object is:
4 2 5 1 3