【位运算】移位操作实现乘法运算

import java.util.Scanner;

/**
 * 功能：用位运算，实现乘法运算，但仅限于乘数是偶数。
 */
public class Main2 {

    public int powerN(int m, int n) {
        while (n > 0) {
            m = m << 1;
            n--;
        }
        return m;
    }

    public static void main(String[] args) {

        Main2 main2 = new Main2();
        Scanner scanner = new Scanner(System.in);

        int input = 0;
        int n = 0;

        while (scanner.hasNext()) {
            input = scanner.nextInt();

            if (input == 0 || input % 2 == 1) {
                System.out.println("the intput value is invalid!");
                continue;
            }

            n = 0;

            while (input != 1) {
                n++;
                input = input / 2;
            }

            System.out.println(main2.powerN(2, n));
        }
    }
}