LeetCode.342. Power of Four

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example:
Given num = 16, return true. Given num = 5, return false.

Follow up: Could you solve it without loops/recursion?

public class Solution {
    public boolean isPowerOfFour(int num) {
       double x=Math.log(num)/Math.log(4);
        int y=(int)x;
     return(x==y);
    }
}