Converting streams to arrays and collections in Java Streams API

15 Sep 2023

StreamsAPI

The Java Streams API introduced in Java 8 has made working with collections and data manipulation much easier and more streamlined. One common task you may encounter when working with streams is the need to convert a stream into an array or a collection. In this blog post, we will explore different ways to accomplish this using the Java Streams API.

Converting Stream to an Array

To convert a stream to an array, Java provides a convenient method toArray() in the Stream interface. Here’s an example of how you can convert a stream of integers to an array:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
Stream<Integer> stream = numbers.stream();

Integer[] numberArray = stream.toArray(Integer[]::new);

In the example above, we start with a List of integers and convert it to a stream using the stream() method. Then we use the toArray() method on the stream, passing in a constructor reference to specify the type of array we want to create. This will convert the stream to an array of integers.

Alternatively, if you want to convert a stream of objects to an array, you can use the toArray() method without passing any arguments:

Stream<String> stream = Stream.of("apple", "banana", "orange");
String[] fruitArray = stream.toArray(String[]::new);

Converting Stream to a Collection

Converting a stream to a collection is equally straightforward in the Java Streams API. You can use the collect() method along with a Collector implementation to convert a stream into a collection. Here’s an example:

List<Integer> numbersList = Stream.of(1, 2, 3, 4, 5)
                                .collect(Collectors.toList());

In the example above, we start with a stream of integers and use the collect() method with Collectors.toList() to convert the stream into a List of integers.

If you want to convert a stream to a different type of collection, such as a Set or a Map, you can use other collectors available in the Collectors class, such as Collectors.toSet() or Collectors.toMap().

Conclusion

Converting streams to arrays and collections can be done easily using the Java Streams API. By using the toArray() method and the collect() method with the appropriate Collector, you can effortlessly convert streams to arrays or different types of collections. This flexibility and convenience provided by the Streams API make it a powerful tool for data manipulation and processing in Java.

#Java #StreamsAPI