Java8 Streams features and Stream creation examples

Java streams are a powerful feature introduced in Java 8 that allow for functional-style programming and operations on data in collections. Some key features of Java streams include:

• Laziness: Stream operations are not executed until a terminal operation (such as forEach or reduce) is called. This allows for operations to be chained together and executed only when necessary.
• Pipelining: Stream operations are performed in a “pipeline” fashion, with the output of one operation becoming the input of the next.
• Immutability: Streams do not modify the underlying data, but instead return new streams with the result of the operation.
• Functional in nature
• Consumable
• No Intermediate Store

Multiple ways to create Streams:

Java 8 streams can be created from various sources, such as collections, arrays, and I/O channels. Here are some examples of creating streams in Java 8:

• Creating a stream from a collection:

Using the stream() method: This method is available on the Collection interface, so you can use it to convert any Collection (such as List, Set, Queue) to a Stream.

List<String> words = Arrays.asList("Java", "Streams", "are", "powerful");
Stream<String> stream = words.stream();

• Using Stream of:

This method is available on the Stream class and it can create a stream from any number of elements.

           Stream<Integer> stream = Stream.of(1, 2, 3, 4, 5);

• Using the iterate() method: This method is available on the Stream class and it creates an infinite stream of elements by applying the given function to the previous element.

           Stream<Integer> naturalNumbers = Stream.iterate(0, n -> n + 1);

• Creating a stream from an array:

int[] numbers = {1, 2, 3, 4, 5};
IntStream intStream = Arrays.stream(numbers);

• Using the generate() method: This method is also available on the Stream class and it creates an infinite stream of elements by applying the given supplier function.

Stream<String> randomStrings = Stream.generate(() -> UUID.randomUUID().toString());

• Using the parallelStream() method: This method is available on the Collection interface, it creates a parallel stream of elements, which can be processed in parallel using multiple threads.

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

• Creating a stream from a file:

try (Stream<String> lines = Files.lines(Paths.get("file.txt"), StandardCharsets.UTF_8)) {
    lines.forEach(System.out::println);
} catch (IOException e) {
    e.printStackTrace();
}

• Creating an empty stream

Stream<String> emptyStream = Stream.empty();

• Creating a stream of a specific size with a specific value

Stream<Integer> stream = Stream.generate(() -> 2).limit(5);

• Creating a stream with a range of values

IntStream intStream = IntStream.range(1, 5);

• Using Buffer Reader

BufferedReader.lines()

• Zip and Jar File

ZipFile.stream()  
JarFile.stream()