Checking if a number can be written as power of 2

PowerOf2Util3.java

/**
 * Problem: Given an integer, i, find whether it can be expressed as 2^k. Where k< i
 */
class PowerOf2Util3 {

    /**
     * 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(log n)
     * Space complexity : 0(1)
     */
    private static boolean isPowerOf2Number(int input){
        if(input<0) input=-1*input;
        if(input==1) return true;

        while (input > 2 && input % 2 == 0) {
            input = input / 2;
        }
        
        return (input == 2);
    }
}