Java – Check whether number is Even or Odd ?

May 13, 2022 SJ Java Basics 0

In this article, we will write a simple Java program to check whether passed/input number is Even or Odd

Find Even and Odd numbers :

  1. Using traditional for–loop and if–else construct
  2. Using Java 8 Stream.filter() method and and if-else construct
  3. Using Java 8 Stream.forEach() method and List
  4. Using Java 8 Stream.forEach() method and StringBuilder

1. Using traditional for-loop and if-else construct :

  • We will evaluate the given number using if-else statements,
    1. If number is divided by 2 and remainder is Zero then number is Even
    2. Else number is Odd

CheckNumberEvenOrOddOrZero.java

package in.bench.resources.numbers;

public class CheckNumberEvenOrOddOrZero {

	// main method
	public static void main(String[] args) {

		checkNumberIsEvenOrOdd(19); // odd
		checkNumberIsEvenOrOdd(0); // zero
		checkNumberIsEvenOrOdd(20); // even
	}


	/**
	 * This method prints whether number is Odd or Even or Zero
	 * 
	 * @param number
	 */
	public static void checkNumberIsEvenOrOdd(int number) {

		if(number%2 == 0) {

			// number is Even
			System.out.println(number + " is an Even number !!");
		}
		else {

			// number is Odd
			System.out.println(number + " is an Odd number !!");
		}
	}
}

Output:

19 is an Odd number !!
0 is an Even number !!
20 is an Even number !!

2. Using Java 8 Stream.filter() method and if-else construct :

  • Using Java 8 Stream, it is very easy to iterate and filter even numbers in a single expression/statement
  • Note: if same stream used to find to Odd numbers then java.lang.IllegalStateException exception is thrown stating “stream has already been operated upon or closed“

FindOddEvenNumber.java

package in.bench.resources.java8.numbers;

import java.util.stream.IntStream;

public class FindOddEvenNumber {

	public static void main(String[] args) {

		// Create IntStream from 1 to 50
		IntStream intStream = IntStream.range(1, 50);


		// print even numbers
		System.out.println("Even numbers :- ");
		intStream
		.filter(num -> (num % 2 == 0))
		.forEach(even -> System.out.print(even + " "));


		// print odd numbers
		//		System.out.println("Odd numbers :- ");
		//		intStream
		//		.filter(num -> (num % 2 != 0))
		//		.forEach(odd -> System.out.print(odd + " "));
	}
}

Output:

Even numbers :- 
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48

3. Using Java 8 Stream.forEach() method and List :

  • Using Java 8 Stream, it is very easy to iterate using Stream.forEach() method and build logic for even/odd numbers and store the results into a List as shown in the below illustration

FindOddEvenNumber.java

package in.bench.resources.arrays.find.number;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.IntStream;

public class FindOddEvenNumber {

	public static void main(String[] args) {

		// 1. declare list to store odd/even numbers
		List<Integer> oddNumbers = new ArrayList<>();
		List<Integer> evenNumbers = new ArrayList<>();


		// 2. Create IntStream from 1 to 50
		IntStream intStream = IntStream.range(1, 50);


		// 3. Check & print even/odd numbers
		intStream
		.forEach(n -> {
			if(n % 2 == 0) {
				evenNumbers.add(n);
			} else {
				oddNumbers.add(n);
			}
		});


		// 4. print odd/even numbers to the console
		System.out.println("Even numbers :- \n" + evenNumbers);
		System.out.print("\nOdd numbers :- \n" + oddNumbers);
	}
}

Output:

Even numbers :- 
[2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48]

Odd numbers :- 
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49]

4. Using Java 8 Stream.forEach() method and StringBuilder :

  • This illustration is very same like the previous example 3 except that instead of storing even/odd numbers in List append those numbers in separate StringBuilder object

FindOddEvenNumber2.java

package in.bench.resources.arrays.find.number;

import java.util.stream.IntStream;

public class FindOddEvenNumber2 {

	public static void main(String[] args) {

		// 1. declare StringBuilder to store odd/even numbers
		StringBuilder sbdEven = new StringBuilder();
		StringBuilder sbdOdd = new StringBuilder();


		// 2. Create IntStream from 1 to 50
		IntStream intStream = IntStream.range(1, 50);


		// 3. Check & print even/odd numbers
		intStream
		.forEach(n -> {
			if(n % 2 == 0) {
				sbdEven.append(n).append(" ");
			} else {
				sbdOdd.append(n).append(" ");
			}
		});


		// 4. print odd/even numbers to the console
		System.out.println("Even numbers :- \n" + sbdEven.toString().trim());
		System.out.print("\nOdd numbers :- \n" + sbdOdd.toString().trim());
	}
}

Output:

Even numbers :- 
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48

Odd numbers :- 
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49

Related Articles :

References :

Happy Coding !!
Happy Learning !!

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