leetcode - Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

public class Solution {    public int singleNumber(int[] A) {        if(A==null || A.length==0){            return 0;        }        int result = A[0];        for(int i=1; i<A.length; i++){            result = result ^ A[i];        }                return result;    }}