# Java: Check whether an given integer is power of 2 or not using O(1) time

## Java Basic: Exercise-205 with Solution

Write a Java program to check whether an integer is a power of 2 or not using O(1) time.

Note: O(1) means that it takes a constant time, like 12 nanoseconds, or two minutes no matter the amount of data in the set.

O(n) means it takes an amount of time linear with the size of the set, so a set twice the size will take twice the time. You probably don't want to put a million objects into one of these.

**Visualization of powers of two from 1 to 1024:**

**Sample Solution:**

**Java Code:**

```
import java.util.*;
public class Main {
public static void main(String[] args) {
// Initialize a boolean variable
boolean b = true;
// Create a Scanner object for user input
Scanner in = new Scanner(System.in);
// Prompt the user to input a number
System.out.print("Input a number: ");
int num = in.nextInt();
// Start a block of code
{
// Continue looping until num becomes 1
while (num != 1) {
// Check if num is odd
if (num % 2 != 0) {
// Toggle the boolean variable
b = !b;
// Print the current value of the boolean variable and exit the program
System.out.print(b);
System.exit(0);
}
// Divide num by 2
num = num / 2;
}
// Print the final value of the boolean variable
System.out.print(b);
}
}
}
```

Sample Output:

Input a number : 25 false

**Flowchart: **

**Java Code Editor:**

** Contribute your code and comments through Disqus.**

**Previous:** Compute x^{n} % y where x, y and n are all 32bit integers.

**Next:** Generate a crc32 checksum of a given string or byte array.

**What is the difficulty level of this exercise?**

Test your Programming skills with w3resource's quiz.

**Weekly Trends and Language Statistics**- Weekly Trends and Language Statistics