怎样知道一个数字是不是2的乘方？

回答了上一篇日志中的一个问题：怎样知道一个数字是不是2的乘方？

在网上搜索了一下，自己总结后，整理出三个方法，代码如下：

package testPass;

/**
 *for positive integer only!
 *@author 孙如意 [e-mail] 
 */
public class IsPowerOfTwo {

 public static void main (String args[]){

  System.out.println("the method of regular expersion: 128 is a power of 2 ? " + method1(128));
  System.out.println("the method of bit operation: 128 is a power of 2 ? " + method2(128));
  System.out.println("the method of mod operation: 128 is a power of 2 ? " + method3(128));
 }

 /**
  * based on regular expression
  * @param num 
  * @return wheather the num is a power of two
  */
 public static boolean method1(Integer num){
  String binNum = Integer.toBinaryString(num);
  //a number which is a power of 2 in binary has only one 1 and starts with it
  return binNum.matches("10*");
 }
 
 /**
  * based on bit operation
  * @param num
  * @return wheather the num is a power of two
  */
 public static boolean method2(Integer num) {
  if ((num & (num-1)) == 0) {
   return true;
  }
  return false;
 }
 
 /**
  * based on mod operation
  * @param num
  * @return wheather the num is a power of two
  */
 public static boolean method3 (Integer num) {
  if(num > 0){
   while(num > 0){
    if (num % 2 == 1) {
     return false;
    }else {
     num /= 2;
     if(num == 1 ) {
      return true;
     }
    }
   } 
  }
  return false;
 }
}