Streams - Beginning Java 8 Language Features - page 616

Table 13-1. List of Commonly Used Stream Operations Supported by the Streams API

Operation Type Description

Returns a stream consisting of the distinct elements of this stream. Elements e1
and e2 are considered equal if e1.equals(e2) returns true.

Distinct Intermediate

filter Intermediate Returns a stream consisting of the elements of this stream that match the

specified predicate.

flatMap Intermediate Returns a stream consisting of the results of applying the specified function

to the elements of this stream. The function produces a stream for each input
element and the output streams are flattened. Performs one-to-many mapping.

limit Intermediate Returns a stream consisting of the elements of this stream, truncated to be no

longer than the specified size.

map Intermediate Returns a stream consisting of the results of applying the specified function to

the elements of this stream. Performs one-to-one mapping.

peek Intermediate Returns a stream whose elements consist of this stream. It applies the specified

action as it consumes elements of this stream. It is mainly used for debugging
purposes.

Discards the first n elements of the stream and returns the remaining stream.
If this stream contains fewer than n elements, an empty stream is returned.

skip Intermediate

sorted Intermediate Returns a stream consisting of the elements of this stream, sorted according to

natural order or the specified Comparator . For an ordered stream, the sort is
stable.

allMatch Terminal Returns true if all elements in the stream match the specified predicate, false

otherwise. Returns true if the stream is empty.

anyMatch Terminal Returns true if any element in the stream matches the specified predicate, false

otherwise. Returns false if the stream is empty.

Returns any element from the stream. An empty Optional object is for an empty
stream.

findAny Terminal

findFirst Terminal Returns the first element of the stream. For an ordered stream, it returns the first

element in the encounter order; for an unordered stream, it returns any element.

noneMatch Terminal Returns true if no elements in the stream match the specified predicate, false

otherwise. Returns true if the stream is empty.

forEach Terminal Applies an action for each element in the stream.

reduce Terminal Applies a reduction operation to computes a single value from the stream.

Debugging a Stream Pipeline
You apply a sequence of operations on a stream. Each operation transforms the elements of the input stream either
producing another stream or a result. Sometimes you may need to look at the elements of the streams as they pass
through the pipeline. You can do so by using the peek(Consumer<? super T> action) method of the Stream<T>
interface that is meant only for debugging purposes. It produces a stream after applying an action on each input
element. The IntStream , LongStream , and DoubleStream also contain a peek() method that takes a IntConsumer ,
a LongConsumer , and a DoubleConsumer as an argument. Typically, you use a lambda expression with the peek()
method to log messages describing elements being processed.