BinaryTree.java

import java.util.Scanner;
public class BinaryTree {
    public BinaryTree(){}
    private static class Node{
        int value;
        Node left;
        Node right;
        public Node(int value){
            this.value=value;
        }}
    private Node root;
    public void populate(Scanner sc){
        System.out.print("Enter the root node: ");
        int value=sc.nextInt();
        root=new Node(value);
        populate(sc, root);
    }
    private void populate(Scanner sc, Node node){
        while(true){
            System.out.println("Currently at node: " + node.value);
            System.out.println("Press 'l' to insert to left, 'r' to insert to right & 'x' to stop inserting here: ");
        char ch=sc.next().charAt(0);
        if(ch=='l'){
            if(node.left==null){
            System.out.println("Enter the value of the left of "+ node.value + ":");
            int value=sc.nextInt();
            node.left=new Node(value);
            populate(sc, node.left);
        } else{
                System.out.println("Left child of "+node.value+" already exists.");
            }}
        else if(ch=='r'){
            if(node.right==null){
            System.out.println("Enter the value of the right of "+node.value);
            int value=sc.nextInt();
            node.right=new Node(value);
            populate(sc, node.right);
        } else{
                System.out.println("Right child of "+node.value+" already exists.");
            }}
        else if(ch=='x'){ return; }
        else{
            System.out.println("Invalid input");
    }}}
    public void display(){
        System.out.println("The tree is: ");
        display(root,0);
        System.out.println("Pre-Order traversal of the tree is: ");
        preOrder();
        System.out.println("\nIn-Order traversal of the tree is: ");
        inOrder();
        System.out.println("\nPost-Order traversal of the tree is: ");
        postOrder();
    }
    private void display(Node node, int level) {
        if (node == null) return;
        display(node.right, level + 1);
        if (level != 0) {
            for (int i = 0; i < level-1; i++) {
                System.out.print("|\t\t");
            }
            System.out.println("|---->" + node.value);
        } else {
            System.out.println(node.value);
        }
        display(node.left, level + 1);
    }
    public void preOrder(){
        preOrder(root);
    }
    private void preOrder(Node node){
        if (node == null) return;
        System.out.print(node.value + " ");
        preOrder(node.left);
        preOrder(node.right);
    }
    public void inOrder(){
        inOrder(root);
    }
    private void inOrder(Node node){
        if (node == null) return;
        inOrder(node.left);
        System.out.print(node.value + " ");
        inOrder(node.right);
    }
    public void postOrder(){
        postOrder(root);
    }
    private void postOrder(Node node){
        if (node == null) return;
        postOrder(node.left);
        postOrder(node.right);
        System.out.print(node.value + " ");
    }
    public static void main(String[] args) {
      Scanner sc=new Scanner(System.in);
      BinaryTree tree=new BinaryTree();
      tree.populate(sc);
      tree.display();
    }}