Java- Sort Even Number First and Maintain the Order

By Atul Rai | Last Updated: April 19, 2024 Previous

Sort Even Number First and Maintain the Order in Java: You have an array of integers with mixed numbers i.e. even & odd, write a program in Java to sort the even numbers first then odd, and maintain the order of numbers.

Example:

int[] arr = {3, 1, 4, 2, 5, 6, 7, 8};
       
Output: 4 2 6 8 3 1 5 7

You can achieve this using Java 8 streams and lambda expressions. Here’s how:

package org.websparrow;

import java.util.Arrays;
import java.util.Comparator;

public class SortEvenFirst {

    public static void main(String[] args) {
        
        int[] arr = {3, 1, 4, 2, 5, 6, 7, 8};
        int[] sortedArr = customSort(arr);
        Arrays.stream(sortedArr).forEach(num -> System.out.print(num + " "));
    }

    public static int[] customSort(int[] arr) {
        return Arrays.stream(arr)
                .boxed() // Convert int to Integer
                .sorted(Comparator.comparingInt(num -> num % 2 == 0 ? 0 : 1)) // Sort even before odd
                .mapToInt(Integer::intValue) // Convert Integer back to int
                .toArray(); // Convert Stream to array
    }
}

Output:

4 2 6 8 3 1 5 7

References

1. Java 8 – How to sort Set with stream.sorted()
2. How to sort list in Java 8
3. Lambda Expressions in Java 8