Checking if a number can be written as power of 2 using bitwise operations

PowerOf2Util2.java

/**
 * Problem: Given an integer, i, find whether it can be expressed as 2^k. Where k< i
 */
class PowerOf2Util2 {

    /**
     * Test
     */
    public static void main(String[] args) {
        int input = 262144; // 2^18
        System.out.print( input + " can be written as power of 2 ? " );
        System.out.println( isPowerOf2Number(input) );
    }

    /**
     * Time complexity: O(1)
     * Space complexity : 0(1)
     */
    private static boolean isPowerOf2Number(int input){
        if(input==0) return false;
        if(input<0) input=-1*input;

        int result = input&(input-1);
        return result==0;
    }
}