# Java – How to Create a Binary Search Tree

This article represents the high level concept and code samples which could be used to create a binary search tree in Java. Please feel free to comment/suggest if I missed to mention one or more important points. Also, sorry for the typos.

• What is a binary search tree?
• What are different kind of traversals?
• Code Samples

###### What is a binary search tree?

A binary search tree is a binary tree in which every node contains a key that satisfies following criteria:

• The key in left child is less than the key in the parent node
• The key in the right child is more than the parent node
• The left and right child are again binary search trees.

Following diagram represents a binary search tree:

###### What are different kind of traversals?

Following are three different kind of traversals:

• Preorder traversal: In preorder traversal, the node is visted first and then, left and right sub-trees.
• Inorder traversal: In inorder traversal, the node is visited between left and right sub-tree.
• Postorder traversal: In postorder traversal, the node is visited after left and right subtrees.

###### Code Sample – How to Create a Binary Search Tree

If the numbers such as {20, 15, 200, 25, -5, 0, 100, 20, 12, 126, 1000, -150} are to be stored in a BinaryTree (represented by code below), following would get printed using different kind of traversal mechanism:

		//Preorder traversal
20, 15, -5, -150, 0, 12, 200, 25, 20, 100, 126, 1000

// Inorder traversal
-150, -5, 0, 12, 15, 20, 20, 25, 100, 126, 200, 1000

//Postorder traversal
-150, 12, 0, -5, 15, 20, 126, 100, 25, 1000, 200, 20


Following is the code for creating binary tree that uses following BinaryTree class and traversals:

		BinaryTree tree = new BinaryTree( 20 );
int[] nums = {15, 200, 25, -5, 0, 100, 20, 12, 126, 1000, -150};
for(int i : nums ) {
}

tree.traversePreOrder();
tree.traverseInOrder();
tree.traversePostOrder();


Following is the code for BinaryTree class:

	public class BinaryTree {

private int data;
private BinaryTree left;
private BinaryTree right;

public BinaryTree(int num) {
this.data = num;
this.left = null;
this.right = null;
}
// As a convention, if the key to be inserted is less than the key of root node, then key is inserted in
// left sub-tree; If key is greater, it is inserted in right sub-tree. If it is equal, as a convention, it
// is inserted in right sub-tree
if (num < this.data) {
if (this.left != null) {
} else {
this.left = new BinaryTree(num);
}

} else {
if (this.right != null) {
} else {
this.right = new BinaryTree(num);
}

}
}
// Visit the node first, then left and right sub-trees
public void traversePreOrder() {
System.out.println( this.data );
if( this.left != null ) {
this.left.traversePreOrder();
}
if( this.right != null ) {
this.right.traversePreOrder();
}
}
// Visit left sub-tree, then node and then, right sub-tree
public void traverseInOrder() {
if( this.left != null ) {
this.left.traverseInOrder();
}
System.out.println( this.data );
if( this.right != null ) {
this.right.traverseInOrder();
}
}
// Visit left sub-tree, then right sub-tree and then the node
public void traversePostOrder() {
if( this.left != null ) {
this.left.traversePostOrder();
}
if( this.right != null ) {
this.right.traversePostOrder();
}
System.out.println( this.data );
}

}



## Ajitesh Kumar

I have been recently working in the area of Data analytics including Data Science and Machine Learning / Deep Learning. I am also passionate about different technologies including programming languages such as Java/JEE, Javascript, Python, R, Julia, etc, and technologies such as Blockchain, mobile computing, cloud-native technologies, application security, cloud computing platforms, big data, etc. I would love to connect with you on Linkedin. Check out my latest book titled as First Principles Thinking: Building winning products using first principles thinking.
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