Java 8 – How to Convert Array of Integers to Stream

Introduction

In Java 8, converting an array of integers to a stream allows you to process the array elements using the Stream API's functional operations such as map(), filter(), and collect(). The Stream API provides an efficient way to manipulate collections or arrays in a more readable and concise manner. To convert an array of integers into a stream, Java offers two common methods: Arrays.stream() and Stream.of().

In this guide, we will explore both methods to convert an array of integers to a stream and demonstrate how to apply some common stream operations.

Solution Steps

1. Define the Array: Create an array of integers to be processed.
2. Convert Array to Stream Using Arrays.stream(): Use the Arrays.stream() method to convert the array to an IntStream.
3. Convert Array to Stream Using Stream.of(): Alternatively, use Stream.of() to convert the array into a Stream<Integer>.
4. Process the Stream: Apply operations like filter(), map(), or collect() on the stream.
5. Display or Collect the Result: Print or collect the processed elements.

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Java Program

Example 1: Using Arrays.stream() for Primitive Int Array

import java.util.Arrays;
import java.util.stream.IntStream;

public class ArrayToIntStreamExample {
    public static void main(String[] args) {
        // Step 1: Define an array of primitive integers
        int[] numbers = {1, 2, 3, 4, 5};

        // Step 2: Convert the array to an IntStream using Arrays.stream()
        IntStream numberStream = Arrays.stream(numbers);

        // Step 3: Display each element in the stream
        numberStream.forEach(System.out::println);
    }
}

Output

1
2
3
4
5

Explanation

Step 1: Define the Array

We define a primitive integer array:

int[] numbers = {1, 2, 3, 4, 5};

Step 2: Convert the Array to an IntStream

We use Arrays.stream() to convert the array into an IntStream:

IntStream numberStream = Arrays.stream(numbers);

Step 3: Process the Stream

We use forEach() to print each element in the stream:

numberStream.forEach(System.out::println);

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Example 2: Using Stream.of() for Wrapper Integer Array

import java.util.stream.Stream;

public class ArrayToStreamUsingStreamOf {
    public static void main(String[] args) {
        // Step 1: Define an array of Integer objects (Wrapper class)
        Integer[] numbers = {1, 2, 3, 4, 5};

        // Step 2: Convert the array to a Stream using Stream.of()
        Stream<Integer> numberStream = Stream.of(numbers);

        // Step 3: Display each element in the stream
        numberStream.forEach(System.out::println);
    }
}

Output

1
2
3
4
5

Explanation

Step 1: Define the Array

We define an array of Integer objects (wrapper class for int):

Integer[] numbers = {1, 2, 3, 4, 5};

Step 2: Convert the Array to a Stream

We use Stream.of() to convert the array into a stream of Integer objects:

Stream<Integer> numberStream = Stream.of(numbers);

Step 3: Process the Stream

We use forEach() to print each element in the stream:

numberStream.forEach(System.out::println);

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Example 3: Filtering Even Numbers Using Stream

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class FilterEvenNumbersFromArray {
    public static void main(String[] args) {
        // Step 1: Define an array of integers
        int[] numbers = {10, 15, 20, 25, 30, 35};

        // Step 2: Convert the array to an IntStream and filter even numbers
        List<Integer> evenNumbers = Arrays.stream(numbers)  // Convert to IntStream
                                          .filter(n -> n % 2 == 0)  // Filter even numbers
                                          .boxed()  // Convert from int to Integer
                                          .collect(Collectors.toList());  // Collect to List

        // Step 3: Display the result
        System.out.println(evenNumbers);
    }
}

Output

[10, 20, 30]

Explanation

Step 1: Define the Array

We define an array of integers:

int[] numbers = {10, 15, 20, 25, 30, 35};

Step 2: Convert the Array to an IntStream and Filter Even Numbers

We use Arrays.stream() to convert the array to an IntStream. Then, we apply filter() to retain only even numbers. The boxed() method converts the primitive int values to Integer objects, and collect() gathers the result into a list:

List<Integer> evenNumbers = Arrays.stream(numbers)
                                  .filter(n -> n % 2 == 0)
                                  .boxed()
                                  .collect(Collectors.toList());

Step 3: Display the Result

The list of even numbers is printed:

System.out.println(evenNumbers);

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Conclusion

In Java 8, converting an array of integers into a stream can be done using either Arrays.stream() for primitive int arrays or Stream.of() for wrapper Integer arrays. Once converted into a stream, you can leverage powerful operations like filtering, mapping, and collecting. This allows for more readable and functional code when working with arrays.