if((i & (i-1)) == 0) { i 是2的幂次方}



public class Test {
    public static void main(String args[]) {
        isPowerOfTwo(2);
        isPowerOfTwo(4);
        isPowerOfTwo(6);
        isPowerOfTwo(9);
        isPowerOfTwo(1024);
        isPowerOfTwo(2044);
    }

    private static void isPowerOfTwo(int num) {
        System.out.println();
        System.out.println("num is: " + num);
        if (((num - 1) & num) == 0) {
            System.out.println("The number is a power of two");
        } else {
            System.out.println("The number is a  NOT A power of two");
        }
    }

}

http://stackoverflow.com/questions/5082314/power-of-2-formula-help

http://www.vaughns-1-pagers.com/computer/powers-of-2.htm