Convert an array to a Stream in Java

This post will discuss various methods to convert array to stream in Java.

1. Convert Boxed Array to Stream

A Stream<T> can be constructed from a boxed array using one of the following methods:

⮚ Using Arrays.stream()

// Generic method to convert array to stream in Java 8 and above

public static <T> Stream<T> getStream(T[] arr) {

return Arrays.stream(arr);

}

⮚ Using Stream.of()

// Generic method to convert array to stream in Java 8 and above

public static <T> Stream<T> getStream(T[] arr) {

// `Stream.of()` internally uses `Arrays.stream()`

return Stream.of(arr);

}

⮚ Using List.stream()

// Generic method to convert array to stream in Java 8 and above

public static <T> Stream<T> getStream(T[] arr) {

return Arrays.asList(arr).stream();

}

2. Convert Primitive Array to Stream

When we convert primitive array to stream, we’ll get primitive streams like IntStream, DoubleStream, and LongStream. We can obtain these primitive streams by using one of the following methods:

⮚ Using Arrays.stream()

// Generic method to convert array to stream in Java 8 and above

public static IntStream getStream(int[] arr) {

return Arrays.stream(arr);

}

⮚ Using IntStream.of()

// Generic method to convert array to stream in Java 8 and above

public static IntStream getStream(int[] arr) {

return IntStream.of(arr);

}

Note – Arrays.asList(arr).stream() and Stream.of(arr) will return Stream<int[]> not IntStream.

3. Filter Array using Stream

We can also filter an array to match certain criteria using streams, as shown below:

import java.util.Arrays;

import java.util.stream.Stream;

class Main

{

public static void main(String[] args)

{

String[] arr = { "NYC", "Mexico", "Beijing", "New Delhi", "Tokyo" };

Stream<String> stream = Arrays.asList(arr).stream();

stream.filter(s -> s.startsWith("N"))

.forEach(System.out::println);

}

Download Run Code

Output:

NYC
New Delhi

4. Convert stream back to array

We might often have a stream of elements and want to convert it back to the array. We can easily do so, as shown below:

import java.util.Arrays;

import java.util.stream.Collectors;

import java.util.stream.Stream;

class Main

{

public static void main(String[] args)

{

Stream<String> stream = Stream.of("NYC", "Mexico", "Beijing", "New Delhi", "Tokyo");

String[] str = stream.collect(Collectors.toList()).toArray(new String[0]);

System.out.println(Arrays.toString(str));

}

Download Run Code

Output:

[NYC, Mexico, Beijing, New Delhi, Tokyo]

This is equivalent to:

import java.util.Arrays;

import java.util.stream.Stream;

class Main

{

public static void main(String[] args)

{

Stream<String> stream = Stream.of("NYC", "Mexico", "Beijing", "New Delhi", "Tokyo");

String[] str = stream.toArray(String[]::new);

System.out.println(Arrays.toString(str));

}

Download Run Code

Output:

[NYC, Mexico, Beijing, New Delhi, Tokyo]

That’s all about converting an array to Stream in Java.