How to Convert Stream to Array in Java

1. Using the convertStreamToArray() Method to Convert Stream to Array in Java
2. Use the toArray() Method to Convert Stream to Array in Java
3. Using the mapToInt() Method

A stream is a collection of objects that supports many methods and can be customized to produce our desired results.

On the other hand, an array is a collection of the same data type variables declared with the same name. You can define an array either as the primitive data type or an object of a class.

If you define the array as a primitive data type, actual values will store in a separate memory location. Conversely, if you define the array as an object of a class, the actual Object will store in a heap segment.

Using the convertStreamToArray() Method to Convert Stream to Array in Java

The stream comes with the convertStreamtoArray() method that returns an array along with an element of the stream in an object array.

Algorithm

1. Create a stream of integers first.
2. Convert a stream of integers into an array using the method Stream.toArray().
3. The returned array is of type Object[].
4. Return that array object in the last.

Program

import java.util.*;
import java.util.stream.*;

public class sampleArticle {
  // Function to convert Stream to Array
  public static <D> Object[] convertStreamToArray(Stream<D> stream) {
    return stream.toArray();
  }

  public static void main(String args[]) {
    // Create a stream of integers
    Stream<Integer> stream = Stream.of(2, 4, 6, 8, 10);

    // Convert Stream to array
    Object[] array = convertStreamToArray(stream);

    // Print the array of stream
    System.out.println("Array from Stream: " + Arrays.toString(array));
  }
}

Output:

Array from Stream: [2,4,6,8,10]

Use the toArray() Method to Convert Stream to Array in Java

Another pre-defined java method to convert Java stream into an array is toArray(). This method returns an array that contains elements of the stream. It uses the supplied generator function to allocate space to the returned array and any other arrays required for the partitioned execution of a function.

Algorithm

1. Create the stream.
2. Using the method toArray() to convert the stream into an array. You need to pass the Object []: new as the generator function to allocate space for the returned array to get this job done.
3. Array obtained via this process is of type Object[].
4. Return the Object Array[] in the last.

Program

import java.util.*;
import java.util.stream.*;
public class sampleArticle {
  // defining function that converts stream into an array
  public static <D> Object[] convertStreamToArray(Stream<D> stream) {
    return stream.toArray(Object[] ::new);
  }

  public static void main(String args[]) {
    // Create a stream of integers
    Stream<Integer> stream1 = Stream.of(2, 4, 6, 8, 10);

    // Convert Stream to array
    Object[] array = convertStreamToArray(stream1);

    // Print the array of stream
    System.out.println("Converted array from Stream: " + Arrays.toString(array));
  }
}

Output:

Converted array from Stream: [2,4,6,8,10]

Using the mapToInt() Method

Java 8 Stream comes with the mapToInt() method that returns an integer stream containing elements of the given stream. It is an intermediary process. The intStream thus obtained is then converted into an integer array (int []) using the toArray() method.

Algorithm

1. Create a stream of integers
2. Convert stream of integers into an integer Stream (intStream) using the Stream.mapToInt() method.
3. Convert the resultant stream into an integer array (int []) using the toArray() method.
4. The array obtained through this method is of type integer.
5. Return the integer array (int []) in the last.

Program

import java.util.*;
import java.util.stream.*;

public class sampleArticle {
  // defining function that converts stream into an array
  public static int[] convertStreamToArray(Stream<Integer> stream) {
    return stream.mapToInt(Integer::intValue).toArray();
  }

  public static void main(String args[]) {
    // Create a stream of integers
    Stream<Integer> stream1 = Stream.of(2, 4, 6, 8, 10);

    // Convert Stream to array
    int[] array = convertStreamToArray(stream1);

    // Print the array of stream
    System.out.println("Converted array from Stream: " + Arrays.toString(array));
  }
}

Output:

Converted array from Stream: [2,4,6,8,10]