Collecting data with streams - Java 8 in Action: Lambdas, Streams, and Functional-Style Programming - page 175

Factory
method

Returned type Used to

total, and average.

Example use: IntSummaryStatistics menuStatistics =

menuStream.collect(summarizingInt(Dish::getCalories));

joining String Concatenate the strings resulting from the invocation

of the toString method on each item of the stream.

Example use: String shortMenu = menuStream.map(Dish::getName).collect(joining(", "));

maxBy Optional<T> An Optional wrapping the maximal element in this

stream according to the given comparator or

Optional.empty() if the stream is empty.

Example use: Optional<Dish> fattest = menuStream.collect(maxBy(comparingInt(Dish::getCalories)));

minBy Optional<T> An Optional wrapping the minimal element in this

stream according to the given comparator or
Optional.empty() if the stream is empty.

Example use: Optional<Dish> lightest = menuStream.collect(minBy(comparingInt(Dish::getCalories)));

reducing The type produced by the Reduce the stream to a single value starting from an

reduction operation initial value used as accumulator and iteratively

combining it with each item of the stream using a

BinaryOperator.

Example use: int totalCalories = menuStream.collect(reducing(0, Dish::getCalories, Integer::sum));

collectingAndThen The type returned by the Wrap another collector and apply a transformation

transforming function function to its result.

Example use: int howManyDishes = menuStream.collect(collectingAndThen(toList(), List::size));

groupingBy Map<K, List<T>> Group the items in the stream based on the value of

one of their properties and use those values as keys in

the resulting Map.