【位运算】移位操作实现乘法运算

 1 import java.util.Scanner;
 2 
 3 /**
 4  * 功能：用位运算，实现乘法运算，但仅限于乘数是偶数。
 5  */
 6 public class Main2 {
 7 
 8     public int powerN(int m, int n) {
 9         while (n > 0) {
10             m = m << 1;
11             n--;
12         }
13         return m;
14     }
15 
16     public static void main(String[] args) {
17 
18         Main2 main2 = new Main2();
19         Scanner scanner = new Scanner(System.in);
20 
21         int input = 0;
22         int n = 0;
23 
24         while (scanner.hasNext()) {
25             input = scanner.nextInt();
26 
27             if (input == 0 || input % 2 == 1) {
28                 System.out.println("the intput value is invalid!");
29                 continue;
30             }
31 
32             n = 0;
33 
34             while (input != 1) {
35                 n++;
36                 input = input / 2;
37             }
38 
39             System.out.println(main2.powerN(2, n));
40         }
41     }
42 }