Lightweight-Stream-API

Stream API from Java 8 rewritten on iterators for Android and Java 7. Full API documentation is available here.

Includes

• Functional interfaces (Supplier, Function, Consumer etc);
• Stream/IntStream/LongStream/DoubleStream (without parallel processing, but with a variety of additional methods and with custom operators);
• Optional/OptionalBoolean/OptionalInt/OptionalLong/OptionalDouble classes;
• Fn and Comparators

Usage

Stream.of(/* array | list | set | map | anything based on Iterator/Iterable interface */)
    .filter(..)
    .map(..)
    ...
    .sorted()
    .forEach(..);
Stream.of(value1, value2, value3)...
IntStream.range(0, 10)...

Example project: https://github.com/aNNiMON/Android-Java-8-Stream-Example

Key features

Custom operators

Unlike Java 8 streams, Lightweight-Stream-API provides the ability to apply custom operators.

Stream.of(...)
    .chain(new Reverse<>())
    .forEach(...);

public final class Reverse<T> implements UnaryOperator<Stream<T>> {

    @Override
    public Stream<T> apply(Stream<T> stream) {
        final Iterator<? extends T> iterator = stream.getIterator();
        final ArrayDeque<T> deque = new ArrayDeque<T>();
        while (iterator.hasNext()) {
            deque.addFirst(iterator.next());
        }
        return Stream.of(deque.iterator());
    }
}

You can find more examples here.

Additional operators

In addition to backported Java 8 Stream operators, the library provides:

• skipNull - filters only not null elements

  Stream.of("a", null, "c", "d", null)
      .skipNull() // [a, c, d]

• sortedBy - sorts by extractor function

  // Java 8
  stream.sorted(Comparator.comparing(Person::getName))
  // LSA
  stream.sortedBy(Person::getName)

• groupBy - groups by extractor function

  // Java 8
  stream.collect(Collectors.groupingBy(Person::getName)).entrySet().stream()
  // LSA
  stream.groupBy(Person::getName)

• chunkBy - partitions sorted stream by classifier function

  Stream.of("a", "b", "cd", "ef", "gh", "ij", "klmnn")
      .chunkBy(String::length) // [[a, b], [cd, ef, gh, ij], [klmnn]]

• sliding - partitions stream into fixed-sized list and sliding over the elements

  Stream.rangeClosed(0, 10)
      .sliding(4, 6) // [[0, 1, 2, 3], [6, 7, 8, 9]]

• takeWhile / dropWhile - introduced in Java 9, limits/skips stream by predicate function

  Stream.of("a", "b", "cd", "ef", "g")
      .takeWhile(s -> s.length() == 1) // [a, b]
  Stream.of("a", "b", "cd", "ef", "g")
      .dropWhile(s -> s.length() == 1) // [cd, ef, g]

• scan - iteratively applies accumulation function and returns Stream

  IntStream.range(1, 6)
      .scan((a, b) -> a + b) // [1, 3, 6, 10, 15]

• indexed - adds an index to every element, result is IntPair

  Stream.of("a", "b", "c")
      .indexed() // [(0 : "a"), (1 : "b"), (2 : "c")]

Download

Releases are available in Maven Central

Maven:

<dependency>
  <groupId>com.landawn</groupId>
  <artifactId>stream-lite</artifactId>
  <version>0.8.5</version>
</dependency>

or Gradle:

dependencies {
  ...
  compile 'com.landawn:stream-lite:0.8.5'
  ...
}

Also included version for Java ME. Checkout javame branch.

For use lambda expressions in Java 7 or Android, take a look at Retrolambda repository.