How to Add Odd and Even Numbers into a Single List in Java 8

In this tutorial, we will learn how to add odd and even numbers into a single list in Java 8. Java 8 provides the Stream API , which allows us to combine multiple lists easily using the flatMap() method.

Code Explanation (Step-by-Step)

  • First, we create three lists: EvenNumbers, PrimeNumbers, and OddNumbers.
  • Then, we add all three lists into one parent list using List<List<Integer>>.
  • After that, we use the stream() method to process the parent list.
  • The flatMap() method converts each inner list into a single stream of integers.
  • Finally, we use Collectors.toList() to collect all numbers into one list.
  • The final list contains even, prime, and odd numbers together.
				
					import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class AddListData {

    public static void main(String[] args) {

        List<Integer> evenNumbers = Arrays.asList(12, 14, 16, 18);
        List<Integer> primeNumbers = Arrays.asList(5, 7, 11, 13);
        List<Integer> oddNumbers = Arrays.asList(1, 3, 5);

        List<List<Integer>> numbersList = Arrays.asList(evenNumbers, primeNumbers, oddNumbers);

        List<Integer> combinedNumbers = numbersList.stream()
                .flatMap(List::stream)
                .collect(Collectors.toList());

        System.out.println("Add prime, odd and even numbers into list: " + combinedNumbers);
    }
}

Output :-
Add prime, odd and even numbers into list: [12, 14, 16, 18, 5, 7, 11, 13, 1, 3, 5]

Java Program to Combine Multiple Lists Using Using addAll()

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

public class CombineMultipleLists {

    public static void main(String[] args) {

        List<Integer> evenNumbers = Arrays.asList(12, 14, 16, 18);
        List<Integer> primeNumbers = Arrays.asList(5, 7, 11, 13);
        List<Integer> oddNumbers = Arrays.asList(1, 3, 5);

        List<Integer> combinedList = new ArrayList<>();

        combinedList.addAll(evenNumbers);
        combinedList.addAll(primeNumbers);
        combinedList.addAll(oddNumbers);

        System.out.println("Combined list: " + combinedList);
    }
}

FAQ

How do you combine multiple lists in Java 8?

You can combine multiple lists in Java 8 by using the Stream API with the flatMap() method. It converts multiple inner lists into a single stream and collects the result into one list.

Which Java 8 method is used to merge multiple lists?

The flatMap() method is commonly used to merge multiple lists into a single list in Java 8.

What is the use of Collectors.toList() in Java 8?

Collectors.toList() is used to collect stream elements into a new list.

Can we convert the final list into an array in Java 8?

Yes, we can convert the final list into an array by using the toArray() method.

				
					Integer[] array = combinedList.toArray(new Integer[0]);

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