Checking wether a number can be written as power of 2

Question

What is the most efficient way to check weather a given number can be written as power of 2 or not ?
If possible please give the program approach in C or Java

Ex:

4 —> true
16 —> true
20 —> false
256 —> true

Answer 1

public class Program
{
public static void main(String[] args) {
int num = 534;
int pow2 = 1;
while(pow2<num){
pow2 *= 2;
}
System.out.println(pow2==num) ;
}
}

Answer 2

Find log to base 2. Must be an integer.

Convert to binary.Must have exactly one 1.

Answer 3

Written as power of two or verified as power of two?