D How To Create A Stream?.md

How to Create a Stream?

There are several ways to get a stream:

From a Collection

The most common way. Every Collection has a .stream() method.

var names = List.of("Ali", "Sara", "John");
Stream<String> stream = names.stream();

From an Array

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

From Static Factory Methods

// From individual values
Stream<String> s1 = Stream.of("a", "b", "c");

// An empty stream (useful as a safe default)
Stream<String> empty = Stream.empty();

From Stream.generate() — Infinite Stream

Produces an infinite stream by calling a Supplier repeatedly. Always pair it with limit() to avoid running forever.

var randoms = Stream.generate(Math::random)
        .limit(5)
        .toList();

From Stream.iterate() — Infinite Stream

Produces an infinite stream by repeatedly applying a function to a seed value.

// Java 9+ form with a predicate stop condition
var evens = Stream.iterate(0, n -> n < 20, n -> n + 2)
        .toList();

System.out.println(evens);

Output

[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

From a File (Lines as a Stream)

try (var lines = Files.lines(Path.of("src/test/resources/SonnetI.txt"))) {
    lines.filter(line -> !line.isBlank())
         .forEach(System.out::println);
}

The stream returned by Files.lines() must be closed after use. Use try-with-resources.

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