Maximum Depth of Binary Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
import java.lang.*;
public class Solution {
    public int maxDepth(TreeNode root) {
        int depth1;
        int depth2;
        if(root == null) return 0;
        //左子树的深度
        depth1 = maxDepth(root.right);
        //右子树的深度
        depth2 = maxDepth(root.left);
        return Math.max(depth1,depth2)+1;
    }
}