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✅ Stream Creation Methods Summary

  • A source: This could be a collection, an array, a generator function, or an I/O channel.
# Source Method Finite? Description
1 Collection collection.stream() yes Create stream from collection Example 1
2 Array Arrays.stream(array) yes Create Strean from Arrays Example 2
3 Values Stream.of(varargs) yes Create stream with elements listed in varargs Example 3
4 Infinite Sequence Stream.iterate(seed, unaryOperator) no Create stream by using seed for first element and then calls UnaryOperator for each subsequent element Example 4
5 Infinite Random Stream.generate(supplier) no Create Stream by calling Supplier for each element upon request Example 5
6 File Lines Files.lines(Path) no used to read all lines from a file as a stream of strings, one per line. Example 6
7 Primitive Streams IntStream / LongStream yes Create Stream for Int, Long and double Example 7
8 Parallel Stream collection.parallelStream() yes Create parallel stram from collection Example 8
9 Stream Empty Stream.empty() yes Create Stream with zero element
10 Infinite Sequence Stream.iterate(seed, predicate, unaryOperator) Depend same as before, but stops if predicate return false Example 9

🧪 Examples

Example 1

List<String> names = List.of("Alice", "Bob", "Charlie");
names.stream().forEach(System.out::println);

Example 2

String[] items = {"A", "B", "C"};
Arrays.stream(items).forEach(System.out::println);

Example 3

Stream.of("Java","Python","C++").forEach(System.out::println);

Example 4

Stream.iterate(0,n ->n +2).limit(5).forEach(System.out::println);  // Outputs 0, 2, 4, 6, 8

Example 5

    Stream.generate(Math::random).limit(3).forEach(System.out::println);

Example 6

    Path path = Paths.get("example.txt");
    try(Stream<String> lines = Files.lines(path)){
        lines.forEach(System.out::println);
    }catch(IOException e){
        e.printStackTrace();
    }

⚠️ Requires import java.nio.file.*; and import java.io_nio2.*;

Example 7

    IntStream.range(1,5).forEach(System.out::println); // 1, 2, 3, 4
    DoubleStream.of(1.1,2.2,3.3).forEach(System.out::println);

Example 8

    List<Integer> nums = List.of(1, 2, 3, 4, 5);
    nums.parallelStream().map(n ->n *n).forEach(System.out::println);

Example 9

  • seed: initial element
  • hasNext: condition to continue the stream
  • next: how to compute the next element
Stream.iterate(0,n ->n< 20,n ->n +2)
        .

forEach(System.out::println);

//similar 
/*
   Stream.iterate(0, n -> n + 2)
 .limit(10)
 .forEach(System.out::println);
 */