Stream API call chain can be simplified

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.

This inspection depends on the Java feature 'Stream and Optional API' which is available since Java 8.