java-stream

One of the prime motivations for the introduction of Java streams was to allow parallel operations. This led to a requirement that operations on Java streams such as map and filter be independent of the position of the item in the stream or the items around it. This has the advantage of making it easy … Read more

Yes, using Collection#removeIf(Predicate): Removes all of the elements of this collection that satisfy the given predicate. Note that it will change the given collection, not return a new one. But you can create a copy of the collection and modify that. Also note that the predicate needs to be negated to act as a filter: … Read more

It is generally not necessary to close streams at all. You only need to close streams that use IO resources. From the Stream documentation: Streams have a BaseStream.close() method and implement AutoCloseable, but nearly all stream instances do not actually need to be closed after use. Generally, only streams whose source is an IO channel … Read more

Just flatMap it: public static void main(final String[] args) throws Exception { final Stream<String> stream1 = /*some stream*/ final Stream<String> stream2 = /*some stream*/ final Stream<String> stream3 = /*some stream*/ final Stream<String> stream4 = /*some stream*/ final Stream<String> stream5 = /*some stream*/ final Stream<String> stream = Stream.of(stream1, stream2, stream3, stream4, stream5).flatMap(Function.identity()); } In your example: … Read more

Use the simple groupingBy variant: Map<String, List<Pojo>> map = pojos .stream() .collect( Collectors.groupingBy(Pojo::getKey) );

You need to chain a Collectors.mapping() collector to the Collectors.groupingBy() collector: Map<String, List<Fizz>> collect = docs.stream() .collect(Collectors.groupingBy(DistrictDocument::getCity, Collectors.mapping(d->createFizz(d),Collectors.toList()))); If createFizz(d) would return a List<Fizz, you can flatten it using Java 9’s Collectors.flatMapping: Map<String, List<Fizz>> collect = docs.stream() .collect(Collectors.groupingBy(DistrictDocument::getCity, Collectors.flatMapping(d->createFizz(d).stream(),Collectors.toList()))); If you can’t use Java 9, perhaps using Collectors.toMap will help: Map<String, List<Fizz>> collect = docs.stream() … Read more

Presented below is the full code of the Exceptional class. It has a quite large API which is a pure extension of the Optional API so it can be a drop-in replacement for it in any existing code—except that it isn’t a subtype of the final Optional class. The class can be seen as being … Read more