Java 8 example of Stream.flatMap() function to get a single List containing all elements from a list of lists. Stream flatMap() Examples Example 1: Converting Nested Lists into a Single List

flatMap() operation flattens the stream opposite to map() operation which does not apply flattening.ģ.Each mapped Stream is closed after its contents have been placed into new Stream.The mapper function used for transformation in flatMap() is a stateless function and returns only a stream of new values.It returns a Stream consisting of the results of replacing each element of the given stream with the contents of a mapped stream produced by applying the provided mapping function to each element.flatMap() is an intermediate operation and return a new Stream.LongStream flatMapToLong(Function mapper)ĭoubleStream flatMapToDouble(Function mapper) 2.2. If the streams created after flatMap() operations return above given types then consider using these functions directly. Stream interface has three more similar methods which produce IntStream, LongStream and DoubleStream respectively after the flatMap() operation. The method returns a new stream of objects of type R.mapper is a non-interfering, stateless function to apply to each element which produces a stream of new values.R represents the element type of the new stream.The stream flatMap() method has the following syntax. Stream words = lines.flatMap(line -> Stream.of(line.split(' +'))) Ģ. Stream lines = Files.lines(path, StandardCharsets.UTF_8) The words stream is a fattened version of all streams into a single stream – consisting of all the words in all the lines. In the following example, lines is a stream of lines in the file. Before flattening :, , ]Īfter flattening : After the flattening effect, we will have one result array with all the items from the 3 arrays. In this example, we have an array of 3 arrays. In very layman’s terms, flattening is referred to as merging multiple collections/arrays into one. Stream.flatMap() helps in converting Stream> to Stream.įlatMap() = Flattening + map() 1. The flatMap() operation has the effect of applying a one-to-many transformation to the elements of the Stream and then flattening the resulting elements into a new Stream. The objects are combined from all the collections in the original Stream. The Stream flatMap() method is used to flatten a Stream of collections to a Stream of objects.

Flat map of earth