Java Program to Implement Double Order Traversal of a Binary Tree

This is a Java Program to perform Double Order traversal over binary tree.
Recurse through:
1. Visit root of (sub)tree.
2. Visit left sub-tree.
3. Revisit root of (sub)tree.
4. Visit right sub-tree.

Here is the source code of the Java Program to Implement Double Order Traversal of a Binary Tree. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

//This is a java program to implement doubleorder traversal of the Binary Search Tree
import java.util.Scanner;
 
class BinarySearchTreeNodes
{
    BinarySearchTreeNodes left, right;
    int      data;
 
    public BinarySearchTreeNodes()
    {
        left = null;
        right = null;
        data = 0;
    }
 
    public BinarySearchTreeNodes(int n)
    {
        left = null;
        right = null;
        data = n;
    }
 
    public void setLeft(BinarySearchTreeNodes n)
    {
        left = n;
    }
 
    public void setRight(BinarySearchTreeNodes n)
    {
        right = n;
    }
 
    public BinarySearchTreeNodes getLeft()
    {
        return left;
    }
 
    public BinarySearchTreeNodes getRight()
    {
        return right;
    }
 
    public void setData(int d)
    {
        data = d;
    }
 
    public int getData()
    {
        return data;
    }
}
 
class BinarySearchTree
{
    private BinarySearchTreeNodes root;
 
    public BinarySearchTree()
    {
        root = null;
    }
 
    public boolean isEmpty()
    {
        return root == null;
    }
 
    public void insert(int data)
    {
        root = insert(root, data);
    }
 
    private BinarySearchTreeNodes insert(BinarySearchTreeNodes node, int data)
    {
        if (node == null)
            node = new BinarySearchTreeNodes(data);
        else
        {
            if (data <= node.getData())
                node.left = insert(node.left, data);
            else
                node.right = insert(node.right, data);
        }
        return node;
    }
 
	public void doubleorder()
	{
		doubleorder(root);
	}
 
	private void doubleorder(BinarySearchTreeNodes r)
	{
		if(r != null)
		{
			System.out.print(r.getData() + " ");
			doubleorder(r.getLeft());
			System.out.print(r.getData() + " ");
			doubleorder(r.getRight());
		}
	}
}
 
public class Doubleorder_Traversal
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        BinarySearchTree bst = new BinarySearchTree();
        System.out.println("Enter the first 10 elements of the tree\n");
        int N = 10;
        for (int i = 0; i < N; i++)
            bst.insert(scan.nextInt());
 
        System.out.print("\nDouble-order   : ");
        bst.doubleorder();
 
        scan.close();
    }
}

Output:

$ javac Doubleorder_Traversal.java
$ java Doubleorder_Traversal
 
Enter the first 10 elements of the tree
 
12 10 11 03 15 19 02 01 04 70
 
Double-order   : 12 10 3 2 1 1 2 3 4 4 10 11 11 12 15 15 19 19 70 70