What is optional in java

A container object which may or may not contain a non- null value. If a value is present, isPresent() returns true . If no value is present, the object is considered empty and isPresent() returns false . Additional methods that depend on the presence or absence of a contained value are provided, such as orElse() (returns a default value if no value is present) and ifPresent() (performs an action if a value is present). This is a value-based class; use of identity-sensitive operations (including reference equality ( == ), identity hash code, or synchronization) on instances of Optional may have unpredictable results and should be avoided.

Method Summary

If a value is present, and the value matches the given predicate, returns an Optional describing the value, otherwise returns an empty Optional .

If a value is present, returns the result of applying the given Optional -bearing mapping function to the value, otherwise returns an empty Optional .

If a value is present, performs the given action with the value, otherwise performs the given empty-based action.

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 .

Methods declared in class java.lang.Object

Method Detail

empty

of

ofNullable

get

isPresent

isEmpty

ifPresent

ifPresentOrElse

public void ifPresentOrElse(ConsumerT> action, Runnable emptyAction)

If a value is present, performs the given action with the value, otherwise performs the given empty-based action.

filter

public OptionalT> filter(PredicateT> predicate)

If a value is present, and the value matches the given predicate, returns an Optional describing the value, otherwise returns an empty Optional .

map

public Optional map(FunctionT,? 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 . If the mapping function returns a null result then this method returns an empty Optional .

API Note: This method supports post-processing on Optional values, without the need to explicitly check for a return status. For example, the following code traverses a stream of URIs, selects one that has not yet been processed, and creates a path from that URI, returning an Optional :

 Optional p = uris.stream().filter(uri -> !isProcessedYet(uri)) .findFirst() .map(Paths::get);

flatMap

public Optional flatMap(FunctionT,? extends Optional> 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 . This method is similar to map(Function) , but the mapping function is one whose result is already an Optional , and if invoked, flatMap does not wrap it within an additional Optional .

or

public OptionalT> or(Supplier> supplier)

If a value is present, returns an Optional describing the value, otherwise returns an Optional produced by the supplying function.

stream

If a value is present, returns a sequential Stream containing only that value, otherwise returns an empty Stream .

API Note: This method can be used to transform a Stream of optional elements to a Stream of present value elements:

 Stream> os = .. Stream s = os.flatMap(Optional::stream)

orElse

orElseGet

public T orElseGet(Supplier supplier)

If a value is present, returns the value, otherwise returns the result produced by the supplying function.

orElseThrow

public Throwable> T orElseThrow(Supplier exceptionSupplier) throws X extends Throwable

If a value is present, returns the value, otherwise throws an exception produced by the exception supplying function.

equals

it is also an Optional and;
both instances have no value present or;
the present values are «equal to» each other via equals() .

hashCode

toString

Returns a non-empty string representation of this Optional suitable for debugging. The exact presentation format is unspecified and may vary between implementations and versions.

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Источник

Class Optional

Additional methods that depend on the presence or absence of a contained value are provided, such as orElse() (returns a default value if no value is present) and ifPresent() (performs an action if a value is present).

This is a value-based class; programmers should treat instances that are equal as interchangeable and should not use instances for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail.