This inspection reports stream API call chains which can be simplified. It allows to avoid creating redundant temporary objects when traversing a collection.

The following call chains are replaced by this inspection:

collection.stream().forEach() → collection.forEach()
collection.stream().forEachOrdered() → collection.forEach()
collection.stream().collect(Collectors.toList()) → new ArrayList<>(collection)
collection.stream().collect(Collectors.toSet()) → new HashSet<>(collection)
collection.stream().collect(Collectors.toCollection(CollectionType::new)) → new CollectionType<>(collection)
collection.stream().toArray() → collection.toArray()
Arrays.asList().stream() → Arrays.stream() or Stream.of()
Collections.singleton().stream() → Stream.of()
Collections.singletonList().stream() → Stream.of()
Collections.emptyList().stream() → Stream.empty()
Collections.emptySet().stream() → Stream.empty()
stream.filter().findFirst().isPresent() → stream.anyMatch()
stream.filter().findAny().isPresent() → stream.anyMatch()
stream.collect(Collectors.counting()) → stream.count()
stream.collect(Collectors.maxBy()) → stream.max()
stream.collect(Collectors.minBy()) → stream.min()
stream.collect(Collectors.mapping()) → stream.map().collect()
stream.collect(Collectors.reducing()) → stream.reduce() or Stream.map().reduce()
stream.collect(Collectors.summingInt()) → stream.mapToInt().sum()
stream.collect(Collectors.summingLong()) → stream.mapToLong().sum()
stream.collect(Collectors.summingDouble()) → stream.mapToDouble().sum()
stream.mapToObj(x -> x) → stream.boxed()
!stream.anyMatch() → stream.noneMatch()
!stream.anyMatch(x -> !(...)) → stream.allMatch()
!stream.noneMatch() → stream.anyMatch()
stream.noneMatch(x -> !(...)) → stream.allMatch()
stream.allMatch(x -> !(...)) → stream.noneMatch()
!stream.allMatch(x -> !(...)) → stream.anyMatch()

Note that the replacements semantic may have minor difference in some cases. For example, Collections.synchronizedList(...).stream().forEach() is not synchronized while Collections.synchronizedList(...).forEach() is synchronized. Or collect(Collectors.maxBy()) would return an empty Optional if the resulting element is null while Stream.max() will throw NullPointerException in this case.