Uses of Class
java9.util.Optional

Packages that use Optional

Package	Description
java9.util	Provides some of the new java.util classes and implementations of static and default interface methods added in Java 8 and, in addition, the JEP 269: Convenience Factory Methods for Collections that were introduced in Java 9.
java9.util.stream	Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections.

Uses of Optional in java9.util

Methods in java9.util that return Optional

Modifier and Type	Method and Description
static <T> Optional<T>	Optional.empty() Returns an empty Optional instance.
Optional<T>	Optional.filter(Predicate<? super T> predicate) If a value is present, and the value matches the given predicate, returns an Optional describing the value, otherwise returns an empty Optional.
<U> Optional<U>	Optional.flatMap(Function<? super T,? extends Optional<? extends U>> mapper) If a value is present, returns the result of applying the given Optional-bearing mapping function to the value, otherwise returns an empty Optional.
<U> Optional<U>	Optional.map(Function<? super T,? extends U> mapper) If a value is present, returns an Optional describing (as if by ofNullable(T)) the result of applying the given mapping function to the value, otherwise returns an empty Optional.
static <T> Optional<T>	Optional.of(T value) Returns an Optional describing the given non-null value.
static <T> Optional<T>	Optional.ofNullable(T value) Returns an Optional describing the given value, if non-null, otherwise returns an empty Optional.
Optional<T>	Optional.or(Supplier<? extends Optional<? extends T>> supplier) If a value is present, returns an Optional describing the value, otherwise returns an Optional produced by the supplying function.

Method parameters in java9.util with type arguments of type Optional

Modifier and Type	Method and Description
<U> Optional<U>	Optional.flatMap(Function<? super T,? extends Optional<? extends U>> mapper) If a value is present, returns the result of applying the given Optional-bearing mapping function to the value, otherwise returns an empty Optional.
Optional<T>	Optional.or(Supplier<? extends Optional<? extends T>> supplier) If a value is present, returns an Optional describing the value, otherwise returns an Optional produced by the supplying function.

Uses of Optional in java9.util.stream

Methods in java9.util.stream that return Optional

Modifier and Type	Method and Description
Optional<T>	Stream.findAny() Returns an Optional describing some element of the stream, or an empty Optional if the stream is empty.
Optional<T>	Stream.findFirst() Returns an Optional describing the first element of this stream, or an empty Optional if the stream is empty.
Optional<T>	Stream.max(Comparator<? super T> comparator) Returns the maximum element of this stream according to the provided Comparator.
Optional<T>	Stream.min(Comparator<? super T> comparator) Returns the minimum element of this stream according to the provided Comparator.
Optional<T>	Stream.reduce(BinaryOperator<T> accumulator) Performs a reduction on the elements of this stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any.

Methods in java9.util.stream that return types with arguments of type Optional

Modifier and Type	Method and Description
static <T> Collector<T,?,Optional<T>>	Collectors.maxBy(Comparator<? super T> comparator) Returns a Collector that produces the maximal element according to a given Comparator, described as an Optional<T>.
static <T> Collector<T,?,Optional<T>>	Collectors.minBy(Comparator<? super T> comparator) Returns a Collector that produces the minimal element according to a given Comparator, described as an Optional<T>.
static <T> Collector<T,?,Optional<T>>	Collectors.reducing(BinaryOperator<T> op) Returns a Collector which performs a reduction of its input elements under a specified BinaryOperator.