leetcode--Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    /**This is a fundamental problem on recursive method.<br>
     * @param root --the root node of a tree
     * @return max depth
     * @author Averill Zheng
     * @version 2014-06-03
     * @since JDK 1.7
     */
    public int maxDepth(TreeNode root) {
    	int maxDepth = 0;
		if(root != null){
			if(root.left == null)
				maxDepth = 1 + maxDepth(root.right);
			else if(root.right == null)
				maxDepth = 1 + maxDepth(root.left);
			else
				maxDepth = 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
		}
		return maxDepth;    
    }
}