Java Program to Check Evil Number

Posted in Java Tutorial

Updated on Jan 11, 2024

By Mari Selvan

👁️ 59 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

In the realm of programming, understanding the properties of numbers is a fascinating journey. One interesting concept is that of Evil Numbers.

An Evil Number is a non-negative integer that has an even number of '1' bits in its binary representation.

In this tutorial, we will explore a Java program designed to check whether a given number is an Evil Number.

The program involves converting the decimal number to its binary representation and counting the number of '1' bits.

📄 Example

Let's delve into the Java code that accomplishes this task.

EvilNumberChecker.java

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import java.util.Scanner;

public class EvilNumberChecker {
  // Function to count the number of set bits (1s) in binary representation
  static int countSetBits(int number) {
    int count = 0;

    while (number != 0) {
      count += number & 1;
      number >>= 1;
    }

    return count;
  }

  // Function to check if a number is an Evil Number
  static boolean isEvilNumber(int number) {
    // Count the number of set bits in the binary representation
    int setBitsCount = countSetBits(number);

    // If the count of set bits is even, it is an Evil Number
    return setBitsCount % 2 == 0;
  }

  // Driver program
  public static void main(String[] args) {
    // Replace this value with the number you want to check
    int number = 15;

    // Call the function to check if the number is an Evil Number
    if (isEvilNumber(number))
      System.out.println(number + " is an Evil Number.");
    else
      System.out.println(number + " is not an Evil Number.");
  }
}

💻 Testing the Program

To test the program with different numbers, modify the value of number in the main method.

Output

15 is an Evil Number.

🧠 How the Program Works

The program defines a class EvilNumberChecker containing a static method countSetBits that takes an integer number as input and returns the count of set bits (1s) in its binary representation.
The static method isEvilNumber checks if the count of set bits is even, indicating that the number is an Evil Number.
Inside the main method, replace the value of number with the desired number you want to check.
The program calls the isEvilNumber method and prints the result.

📏 Between the Given Range

Let's explore the Java code that checks for Evil Numbers in the specified range.

EvilNumberChecker.java

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public class EvilNumberChecker {

  // Function to check if a number is Evil
  static boolean isEvilNumber(int num) {
    int binaryOnes = Integer.bitCount(num);
    return binaryOnes % 2 == 0;
  }

  // Driver program
  public static void main(String[] args) {
    System.out.println("Evil numbers in the range 1 to 10:");

    // Check for Evil Numbers in the range 1 to 10
    for (int i = 1; i <= 10; i++) {
      if (isEvilNumber(i)) {
        System.out.print(i + " ");
      }
    }
  }
}

💻 Testing the Program

Output

Evil numbers in the range 1 to 10:
3 5 6 9 10

Compile and run the program to see the Evil Numbers in the specified range.

🧠 How the Program Works

The program defines a class EvilNumberChecker containing a static method isEvilNumber that checks if a given number is an Evil Number.
Inside the method, it uses Integer.bitCount to count the number of set bits (1s) in the binary representation of the number.
The main function tests the Evil Number check for numbers in the range 1 to 10 and prints the Evil Numbers.

🧐 Understanding the Concept of Evil Number

Before delving into the code, let's understand the concept of Evil Numbers. An Evil Number is a non-negative integer that has an even number of '1' bits in its binary representation.