Double the even/odd numbers ArrayList using Java 8 Streams

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In this post, we will see how to double the even and odd numbers present in an ArrayList separately with the help of Java 8 Streams.

Let’s say: There is an ArrayList of 10 integer values as shown below. In the first example, using Streams, we are going to double each even integer of the ArrayList and In the second example, we are going to double odd integers.

List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);

1	List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);

Example 1

/**
 * Double of Even Numbers using Streams
 * @author Deepak Verma
 */
import static java.util.stream.Collectors.toList;
import java.util.Arrays;
import java.util.List;
public class DoubleOfEvenUsingStreams {
	public static void main(String[] args) {
		List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);
		List<Integer> doubleValueListOfEvenIntegers = list.stream()
														  .filter(i -> i%2 == 0)
											              .map(i -> i*2)
											              .collect(toList());
		System.out.println("Double values of Even ArrayList Integers: "+doubleValueListOfEvenIntegers);
	}
}

/**

* Double of Even Numbers using Streams

* @author Deepak Verma

import static java.util.stream.Collectors.toList;

import java.util.Arrays;

import java.util.List;

public class DoubleOfEvenUsingStreams {

public static void main(String[] args) {

List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);

List<Integer> doubleValueListOfEvenIntegers = list.stream()

.filter(i -> i%2 == 0)

.map(i -> i*2)

.collect(toList());

System.out.println("Double values of Even ArrayList Integers: "+doubleValueListOfEvenIntegers);

}

Output:

Double values of Even ArrayList Integers: [4, 8, 12, 16, 20]

1	Double values of Even ArrayList Integers: [4, 8, 12, 16, 20]

Example 2

/**
 * Double of Odd Numbers using Streams
 * @author Deepak Verma
 */
import static java.util.stream.Collectors.toList;
import java.util.Arrays;
import java.util.List;
public class DoubleOfOddUsingStreams {
	public static void main(String[] args) {
		List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);
		List<Integer> doubleValueListOfOddIntegers = list.stream()
														  .filter(i -> i%2 != 0)
											              .map(i -> i*2)
											              .collect(toList());
		System.out.println("Double values of Odd ArrayList Integers: "+doubleValueListOfOddIntegers);
	}
}

/**

* Double of Odd Numbers using Streams

* @author Deepak Verma

import static java.util.stream.Collectors.toList;

import java.util.Arrays;

import java.util.List;

public class DoubleOfOddUsingStreams {

public static void main(String[] args) {

List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);

List<Integer> doubleValueListOfOddIntegers = list.stream()

.filter(i -> i%2 != 0)

.map(i -> i*2)

.collect(toList());

System.out.println("Double values of Odd ArrayList Integers: "+doubleValueListOfOddIntegers);

}

Output:

Double values of Odd ArrayList Integers: [2, 6, 10, 14, 18]

1	Double values of Odd ArrayList Integers: [2, 6, 10, 14, 18]

That’s it. It’s that easy to double the even and odd numbers of ArrayList with the power of Java 8 Streams.

If you like this post, please check out my other similar posts:

How to add/sum up the ArrayList integers using Java8 Streams

Reference:

Java 8 Streams

Author

Deepak Verma
Deepak Verma is a Test Automation Consultant and Software development Engineer for more than 10 years. His mission is to help you become an In-demand full stack automation tester. He is also the founder of Techndeck, a blog and online coaching platform dedicated to helping you succeed with all the automation basics to advanced testing automation tricks.
View all posts
http://Techndeck.com deepak.rkgit@gmail.com Verma Deepak

7 Comments

Bohdan Myslyvchuk on November 17, 2019 at 3:01 pm

Hi, your filter function works only because of List input and ONLY because it has odd and even numbers. If you place there random even numbers, for example 22, 33, 44, 24, 56 – it won’t work it will do pow(x, 2) to all numbers, not only to even. Basically, our code incorrect in terms of what it should do

Deepak Verma on November 17, 2019 at 11:26 pm
Hi Bohdan,
As what I understood, you said if you tried with list items [22, 33, 44, 24, 56], it’s not working as intended.
Well, I tried, it’s working completely fine.
Please correct me if I didn’t understand your question clearly. Kindly, let me know and i’ll try to help out asap.
Thanks
Reply

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Deepak Verma on April 2, 2019 at 7:53 pm
Thank you. I am glad that my content helped you.
Thanks
Reply

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