How to check if number is power of two

public static boolean powerOfTwoGeneral(int n)
 {
 while(n%2==0)
 {
 n=n/2;
 }
 if(n==1)
 {
 return true;
 }
 else
 {
 return false;
 }
 }

Approach 2:

We can use bitwise and operator to check if number is power of two or not.

public static boolean powerOfTwoBitwise(int n)
 {
  return (n & n-1)==0;
 }

It will a very simple way to check if number is power of two. Let’s see how it works.
Let’s say n is 8. Its binary representation will be : 1000.
binary represetation of 7 will be : 0111.
1 0 0 0
& 0 1 1 1
———-
0 0 0 0
———-
If number is power of 2, then it will have only one bit set to “1”.
For example:
8 :   1000
32 : 100000

Similarly when you  check binary form of 7 and 31, it will have all the bits set to “1”
7 :   111
31:  11111
so if you apply bitwise & operator on n and n-1 and result is 0. It means number is power of two.

Java program to check if number is power of two:

package org.arpit.java2blog;

public class PowerOfTwoMain {

 public static void main(String[] args) {
  System.out.println("128 is power of two : "+powerOfTwoGeneral(128));
  System.out.println("64 is power of two : "+powerOfTwoBitwise(64));
  System.out.println("22 is power of two : "+powerOfTwoBitwise(22));
  System.out.println("22 is power of two : "+powerOfTwoGeneral(22));
 }
 // Approach 1
 public static boolean powerOfTwoGeneral(int n)
 {
  while(n%2==0)
  {
   n=n/2;
  }
  if(n==1)
  {
   return true;
  }
  else
  {
   return false;
  }
 }
 // Approach 2
 public static boolean powerOfTwoBitwise(int n)
 {
  return (n & n-1)==0;
 }

}

When you run above code, you will get below results

128 is power of two : true
64 is power of two : true
22 is power of two : false
324 is power of two : false