Square Root More Than 2 in Java

I know its sound simple, but in fact i spent more than 20 minute in Google to find the answer.

By default Java only provide method square root by 2 like this :
double root = Math.sqrt(new Double("4")); // 4 square root by 2, result is 2

If you want square root more than 2, use this :
double root = Math.pow(new Double("8"), new Double("0.3333333")); // 8 square root by 3, result is 2