Find the diameter of the binary tree

The diameter of the tree, sometimes called the width of the tree, is the number of nodes in the longest path between two leaf nodes in the tree

int DiameterOfTree(BinaryTreeNode root,int diameter){
    
    
  int left,right;
  if(root == null)
    return 0;
  left = DiameterOfTree(root.getLeft(),diameter);
  right = DiameterOfTree(root.getRight(),diameter);
  if((left+right)>diameter){
    
    
    diameter = left+right;
  }
  return Math.max(left,right)+1;
}