Java 8 Stream API is a big step towards functional programming and leverages multi-core processors which are ubiquitous nowadays. Stream represents a series of objects sourced from collection and supports data processing queries, SQL like operations.

There are generic interface Stream<T> and three specific interfaces for primitives, DoubleStream, IntStream and LongStream

Difference between Stream<Integer> and IntStream is that: IntStream is for primitives (int, short, byte and char) Stream<Integer> is for Integer wrapper class

Methods to convert between different Streams

Those all map* methods take a single parameter Function as shown below respectively.

It is a stream that can process results simultaneously by using multiple threads. Although performance increase can be achieved, it can change the result unexpectedly if not used carefully.