Evil Number Java

The Evil number is another special positive whole number in Java that has an even number of 1's in its binary equivalent. Unlike Prime and Armstrong numbers, Evil number is not so popular and asked by the interviewers.

The numbers which are not evil are called odious numbers. Let's some examples of evil and odious numbers.

15 is an evil number because in its binary equivalent, i.e., 1111, it has an even number of ones.
16 is an odious number because in its binary equivalent, i.e., 10000 has not even number of ones
23 is also an evil number because it has an even number of ones in its binary equivalent, i.e., 10111.

In order to check whether the number is evil or not, we have to follow the following steps:

We first take a number.
We then find the binary equivalent of this number and store it into another variable.
We find the total number of ones in the binary number.
If we found an even number of ones in the binary equivalent number, then the number is an evil number. Else the given number is not an evil number.

Note: To convert a decimal number into binary, we can use the toBinaryString() in-built method or do it manually by using the loop.

Let's implement the code to check whether the number is evil or not.

EvilNumberExample.java

//import required classes and packages
import Java.util.*; 
import java.io.*; 
import java.util.Scanner;

//create EvilNumberExample class to check whether the given number is an Evil number or not
public class EvilNumberExample {

	// create checkNumber() method that returns true when it founds number Evil 
	public static boolean checkNumber(int n) {

		// find the equivalence binary number using user defined convertToBinary() method
		long binaryNumber = convertToBinary(n);

		// find total number of 1's in binary number
		int count = 0;

		// iterate each digit of binary number
		while(binaryNumber != 0) {

			// if the last digit of binary number is 1, increase the count value
			if(binaryNumber % 10 == 1) 
				count++;

			// remove the last digit from the number
			binaryNumber = binaryNumber / 10;
		}

		// check whether the value of count is even or odd
		if(count % 2 == 0)
			return true;	//return true when the value of count is even

		//return false if the value of the count is false
		return false;
	}

	//create convertToBinary() method to convert the decimal value into binary
	private static long convertToBinary(int number) {
		long binaryNumber = 0;
		int rem = 0;
		int j = 1;
		while(number != 0) {
			rem = number % 2;
			binaryNumber += rem * j;
			number = number / 2;
			j = j * 10;
		}
		
		return binaryNumber;	//return the binary equivalent number of the decimal number
	}
	
	//main() method start
	public static void main(String[] args) {
	
		// declare variable in which the user entered value will be store
		int num = 0;

		// create scanner class object 
		Scanner sc =  new Scanner(System.in);
		
		//display custom message
		System.out.print("Enter a number : ");
		
		//get input from user
		num = sc.nextInt();

		// check whether the number is evil number or not
		if(checkNumber(num))
			System.out.println(num + " is an evil number");
		else
			System.out.println(num + " is not an evil number");

	}
}

Output

Let's implement one more program to get all the Evil numbers in a given range

FindAllEvilNumber.java

//import required classes and packages
import java.util.*; 
import java.io.*; 
import java.util.Scanner;

//create a class to get all the Evil number in a given range
public class FindAllEvilNumber {

	//main() method start
	public static void main(String args[])
	{
		int range;
		
		//create scanner class object
		Scanner sc=new Scanner(System.in);
		
		//show custom message
		System.out.println("Enter the value of range");
		
		//store user entered value into variable range
		range = sc.nextInt();

		for(int i = 1; i <= range; i++)
			if(checkNumber(i)){
				System.out.println(i + " is an Evil number");
			}
	}
	
	// create checkNumber() method that returns true when it founds number Evil 
	public static boolean checkNumber(int n) {

		// find the equivalence binary number using user defined convertToBinary() method
		long binaryNumber = convertToBinary(n);

		// find total number of 1's in binary number
		int count = 0;

		// iterate each digit of binary number
		while(binaryNumber != 0) {

			// if the last digit of binary number is 1, increase the count value
			if(binaryNumber % 10 == 1) 
				count++;

			// remove the last digit from the number
			binaryNumber = binaryNumber / 10;
		}

		// check whether the value of count is even or odd
		if(count % 2 == 0)
			return true;	//return true when the value of count is even

		//return false if the value of the count is false
		return false;
	}

	//create convertToBinary() method to convert the decimal value into binary
	private static long convertToBinary(int number) {
		long binaryNumber = 0;
		int rem = 0;
		int j = 1;
		while(number != 0) {
			rem = number % 2;
			binaryNumber += rem * j;
			number = number / 2;
			j = j * 10;
		}
		
		return binaryNumber;	//return the binary equivalent number of the decimal number
	}
}

Output