Java Data Structure How to - Create Binary Tree

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Question

We would like to know how to create Binary Tree.

Answer

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
/*from   w  w  w  . ja v a  2  s .c  om*/
class TreeNode {
  TreeNode left, right;
  int data;

  TreeNode() {
    data = 0;
    left = right = null;
  }

  TreeNode(int n) {
    data = n;
    left = right = null;
  }

  void disp() {
    System.out.println(data + " ");
  }

  void setLeft(TreeNode n) {
    left = n;
  }

  void setRight(TreeNode n) {
    right = n;
  }

  TreeNode getLeft() {
    return left;
  }

  TreeNode getRight() {
    return right;
  }

  void setData(int d) {
    data = d;
  }

  int getData() {
    return data;
  }
}

class BinaryTree {
  TreeNode root;

  BinaryTree() {
    root = null;
  }

  void insert(int data) {
    root = insert(root, data);
  }

  TreeNode insert(TreeNode node, int data) {
    if (node == null) {
      node = new TreeNode(data);
    } else {
      if (data <= node.data) {
        node.left = insert(node.left, data);
      } else {
        node.right = insert(node.right, data);
      }
    }
    return (node);
  }

  void inorder() {
    inorder(root);
    System.out.println();
  }

  void inorder(TreeNode r) {
    if (r != null) {
      inorder(r.getLeft());
      System.out.print(r.getData() + " ");
      inorder(r.getRight());
    }
  }

  void preorder() {
    preorder(root);
    System.out.println();
  }

  void preorder(TreeNode r) {
    if (r != null) {
      System.out.print(r.getData() + " ");
      preorder(r.getLeft());
      preorder(r.getRight());
    }
  }

  void postorder() {
    postorder(root);
    System.out.println();
  }

  void postorder(TreeNode r) {
    if (r != null) {
      postorder(r.getLeft());
      postorder(r.getRight());
      System.out.print(r.getData() + " ");
    }
  }
}

public class Main {

  public static void main(String[] argv) throws IOException {
    BinaryTree bt = new BinaryTree();
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    int val;
    char ch = ' ';
    String clearbuffer;
    do {
      System.out.print("Enter a number: ");
      val = Integer.parseInt(br.readLine());
      bt.insert(val);
      System.out.print("Do you wish to enter more values (Y/N).....");
      ch = (char) br.read();
      clearbuffer = br.readLine();
    } while (ch == 'y' || ch == 'Y');
    System.out.println("Postorder traversal of given tree is: ");
    bt.postorder();
    System.out.println("Preorder traversal of given tree is: ");
    bt.preorder();
    System.out.println("Inorder traversal of given tree is: ");
    bt.inorder();
  }
}

The code above generates the following result.

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