java.util · java.base · since Java 1.8

Optional

declaration

public final class Optional<T>

A maybe-value return type: forces callers to confront absence. Consume with orElse/map/ifPresent; never bare get(); not for fields or parameters (EJ 55).

Key methods

`static <T> Optional<T> of(T) / ofNullable(T) / empty()`	Creation (of(null) throws).
`boolean isPresent() / boolean isEmpty()`	Presence checks — prefer ifPresent/map/orElse over branching on these when possible.
`T orElse(T other) / T orElseGet(Supplier<T>)`	Defaults — orElse's argument is ALWAYS evaluated.
`T orElseThrow(Supplier<X>)`	Fail with a meaningful exception.
`Optional<T> filter(Predicate<? super T>)`	Keep the value only if it matches the predicate; otherwise becomes empty.
`Optional<U> map(Function) / flatMap(Function)`	Transform if present.
`Optional<T> or(Supplier<? extends Optional<? extends T>>)`	Lazy fallback Optional — the supplier runs only when this Optional is empty.
`void ifPresent(Consumer) / ifPresentOrElse(…)`	Conditional actions.
`Stream<T> stream()`	0-or-1 element stream — flatMap-friendly.