1 package algorithm; 2  3 /** 4  * Created by moi on 2017/10/18. 5  */ 6 public class PowerOf2 { 7  8     public static int powOf2(int n){ 9         if(n==0){10             return 1;11         }12         if(n>31){13             throw new RuntimeException("n>31 is too big.");14         }15         int base = 2;16         while(n>1){17             base = base << 1;18             System.out.println(base);19             n--;20         }21         return base;22     }23 24     public static boolean checkPowerOf2(int n) {25         // write your code here26         boolean flag = true ;27 28         if ( n < 1 ){29             return false;30         }31 32         while( n>= 2 ){33             // 1的二进制是 最低位为1，其余各位为0，所以这里 n & 1 即n的最低位和 1的最低位1 进行与，如果是偶数，结果就是0，奇数就是1.34             if ( (n & 1) == 1 ){35                 flag = false ;36                 break;37             }38             n = n >> 1 ;39         }40         return flag ;41     }42 43     public static void main(String[] args) {44         PowerOf2.powOf2(3);45     }46 }