Is BST balanced- heights of the two sub-trees of any node differs by no more than one

IsBalancedBST.java

 
public class TreeNode{
  int data;
  TreeNode left;
  TreeNode right;
  
  public TreeNode(int d){
      data = d;
      left = null;
      right = null;
  }
}
 
public class BinarySearchTree{
  
 TreeNode root;
 
 public BinarySearchTree{
  root = null;
 }

 public boolean getIsBalanced(){
  if (root == null){
   return false;
  }
  else if (root.left == null && root.right == null){
   return true;
  }
  else{
   return getIsBalancedHelper(root);
  }
 }
 
 private boolean getIsBalancedHelper(TreeNode node){
  if (!node.left && !node.right){
   return true
  }
  else if (node.left != null && node.right == null){
   return (node.left.left == null ? true : false);
  }
  else if (node.left == null && node.right != null){
   return (node.right.right == null ? true : false)
  }
  else{
   boolean left = getIsBalancedHelper(node.left);
   boolean right = getIsBalancedHelper(node.right);
   return (left && right);
  }
 }
 
}