Transforming Data with Java 8 Streams API: Difference between revisions
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=Overview= | =Overview= | ||
The Stream API offers the possibility to intercept a stream and converts its elements into elements of another type, offered also as a stream. This operations is conventionally named [[#Mapping_Data|mapping]]. | The Stream API offers the possibility to intercept a stream and converts its elements into elements of another type, offered also as a stream. This operations is conventionally named [[#Mapping_Data|mapping]]. The world ''mapping'' is used because it has a meaning similar to ''transforming'', but with the nuance of "creating a new version" rather than "modifying". | ||
=Mapping Data= | =Mapping Data= |
Revision as of 18:10, 28 March 2018
Internal
Overview
The Stream API offers the possibility to intercept a stream and converts its elements into elements of another type, offered also as a stream. This operations is conventionally named mapping. The world mapping is used because it has a meaning similar to transforming, but with the nuance of "creating a new version" rather than "modifying".
Mapping Data
The Stream API exposes the map() method, which converts the stream's elements into elements of another type, offered also as a stream. The conversion if performed by a Function<T, R> presented as the argument of the map() method.
map()
map() takes a lambda that transforms an element of a certain type into an element of a different type, by applying a function, and pushing it to the the result stream.
<R> Stream<R> map(Function<? super T, ? extends R> mapper);
flatMap()
flatMap() returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. If a mapped stream is null an empty stream is used, instead.
<R> Stream<R> flatMap(Function<? super T,? extends Stream<? extends R>> mapper)
Example:
List<String> uniqueChars = words.
stream().
map(word -> word.split("")).
flatMap(Arrays::stream).
distinct().
collect(toList());