SimplifyStreamApiCallChains

Reports stream API call chains that can be simplified. Simplification will often avoid some temporary object creation during collection traversal.

The inspection replaces the following call chains:

• collection.stream().forEach() → collection.forEach()
• collection.stream().collect(toList/toSet/toCollection()) → new CollectionType<>(collection)
• collection.stream().toArray() → collection.toArray()
• Arrays.asList().stream() → Arrays.stream() or Stream.of()
• IntStream.range(0, array.length).mapToObj(idx -> array[idx]) → Arrays.stream(array)
• IntStream.range(0, list.size()).mapToObj(idx -> list.get(idx)) → list.stream()
• Collections.singleton().stream() → Stream.of()
• Collections.emptyList().stream() → Stream.empty()
• stream.filter().findFirst().isPresent() → stream.anyMatch()
• stream.collect(counting()) → stream.count()
• stream.collect(maxBy()) → stream.max()
• stream.collect(mapping()) → stream.map().collect()
• stream.collect(reducing()) → stream.reduce()
• stream.collect(summingInt()) → stream.mapToInt().sum()
• stream.mapToObj(x -> x) → stream.boxed()
• stream.map(x -> {...; return x;}) → stream.peek(x -> ...)
• !stream.anyMatch() → stream.noneMatch()
• !stream.anyMatch(x -> !(...)) → stream.allMatch()
• stream.map().anyMatch(Boolean::booleanValue) → stream.anyMatch()
• IntStream.range(expr1, expr2).mapToObj(x -> array[x]) → Arrays.stream(array, expr1, expr2)
• Collection.nCopies(count, ...) → Stream.generate().limit(count)
• stream.sorted(comparator).findFirst() → Stream.min(comparator)
• optional.orElseGet(() -> { throw new ...; }) → optional.orElseThrow()

Note that the replacement semantics may have minor differences in some cases. For example, Collections.synchronizedList(...).stream().forEach() is not synchronized while Collections.synchronizedList(...).forEach() is synchronized. Also, collect(Collectors.maxBy()) returns an empty Optional if the resulting element is null while Stream.max() throws NullPointerException in this case.