ArrayList partition into two lists of odd/even numbers

Problem Statement: Write a Java program to create a method that partitions an ArrayList of integers into two separate lists, one containing even numbers and the other containing odd numbers.

Here’s a Java program that demonstrates how to create a method to partition an ArrayList of integers into two separate lists, one containing even numbers and the other containing odd numbers.

package com.javacodepoint.collection;

import java.util.ArrayList;
import java.util.List;

public class PartitionArrayList {

	public static void main(String[] args) {
		ArrayList<Integer> numbers = new ArrayList<>();
		numbers.add(10);
		numbers.add(25);
		numbers.add(6);
		numbers.add(15);
		numbers.add(30);
		numbers.add(7);

		System.out.println("Original List: " + numbers);

		// Partition the list into even and odd lists
		List<Integer> evenList = new ArrayList<>();
		List<Integer> oddList = new ArrayList<>();
		partitionArrayList(numbers, evenList, oddList);

		System.out.println("Even Numbers List: " + evenList);
		System.out.println("Odd Numbers List: " + oddList);
	}

	// Method to partition an ArrayList into even and odd lists
	public static void partitionArrayList(List<Integer> originalList, List<Integer> evenList, List<Integer> oddList) {
		for (Integer number : originalList) {
			if (number % 2 == 0) {
				evenList.add(number); // Even number, add to even list
			} else {
				oddList.add(number); // Odd number, add to odd list
			}
		}
	}
}

OUTPUT:

Original List: [10, 25, 6, 15, 30, 7]
Even Numbers List: [10, 6, 30]
Odd Numbers List: [25, 15, 7]

Explanation:

1. Creating the List: We create an ArrayList named numbers and populate it with some integers.
2. Printing the Original List: We print the contents of the numbers list using System.out.println().
3. Partitioning the List: We create two new ArrayLists, evenList and oddList, to store even and odd numbers, respectively. We then call the partitionArrayList() method to perform the partitioning.
4. partitionArrayList() Method: This method takes three parameters: the original list (originalList), the list for even numbers (evenList), and the list for odd numbers (oddList).
5. Iterating Through the Original List: We use a for-each loop to iterate through each number in the originalList.
6. Partitioning Even and Odd Numbers: Inside the loop, we check if the number is even or odd using the modulo operator (%). If the remainder when dividing the number by 2 is 0, it’s even and gets added to the evenList. Otherwise, it’s odd and gets added to the oddList.
7. Printing the Result Lists: Finally, we print the contents of both the evenList and oddList to display the partitioned numbers.

By using a method to iterate through the original list and separate even and odd numbers into two different lists, the program effectively partitions the ArrayList into two separate lists while preserving the order of elements.

See also: Find common elements in two ArrayLists in Java.