1071. Greatest Common Divisor of Strings

import java.math.*;
class Solution {
    public String gcdOfStrings(String str1, String str2) {
        if((str1 + str2).equals(str2 + str1) == false)
        {
            return "";
        }
        int len = gcd(str1.length(), str2.length());
        return str1.substring(0, len);
    }

    public static int gcd(int a, int b)
    {
        while(b != 0)
        {
            if(a > b)
            {
                a = a - b;
            }
            else
            {
                b = b - a;
            }
        }
        return a;
    }
}