./curric/Functional-Programming/Java-Streams/

Java Streams ( the functional API for Java Collections )

Java Streams is an API that applies a specific action (filter, map, or reduce) over the entire collection. After applying the specific action, a new modified collection is returned, allowing for method chaining (do operators one after another)

  // Example of Chaining
  originalCollection.firstMethod().secondMethod().finalMethod()
  
  // syntax guidelines state to put a newline 
  // before every new method call for readability 
  originalCollection
      .firstMethod()
      .secondMethod()
      .finalMethod()

Types of Streams

• Stream<T>
  • Generic Stream of type T where T extends Object
• IntStream
  • Stream of type int wrapped in Integer object, and also adding specific syntactic sugar methods such as sum, average, and count
• LongStream
  • Stream of type long wrapped in Long object, and also adding specific syntactic sugar methods such as sum, average, and count
• DoubleStream
  • Stream of type double wrapped in Double object, and also adding specific syntactic sugar methods such as sum, average, and count
• Essential Stream Functions
  • map(Function<? super T,? extends R> mapper)
    • Returns a stream consisting of the results of applying the given function to the elements of this stream.
    • mapToInt(ToIntFunction<? super T> mapper)
      • applies map and specifically returns IntStream
    • mapToDouble(ToDoubleFunction<? super T> mapper)
      • applies map and specifically return DoubleStream
    • mapToLong(ToLongFunction<? super T> mapper)
      • applies map and specifically return LongStream
  • filter(Predicate<? super T> predicate)
    • Returns a stream consisting of the elements of this stream that match the given predicate.
  • forEach(Consumer<? super T> action)
    • Performs an action for each element of this stream.
  • reduce(BinaryOperator<T> accumulator)
    • Performs a reduction on the elements of this stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any.
  • collect(Collector<? super T,A,R> collector)
    • Performs a mutable reduction operation on the elements of this stream using a Collector.

Reference to Oracle Docs for Streams