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Optional

public final class Optional
extends Object

java.lang.Object
   ↳ java.util.Optional<T>


A container object which may or may not contain a non-null value. If a value is present, isPresent() will return true and get() will return the value.

Additional methods that depend on the presence or absence of a contained value are provided, such as orElse() (return a default value if value not present) and ifPresent() (execute a block of code if the value is present).

Summary

Public methods

static <T> Optional<T> empty()

Returns an empty Optional instance.

boolean equals(Object obj)

Indicates whether some other object is "equal to" this Optional.

Optional<T> filter(Predicate<? super T> predicate)

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

<U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper)

If a value is present, apply the provided Optional-bearing mapping function to it, return that result, otherwise return an empty Optional.

T get()

If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.

int hashCode()

Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.

void ifPresent(Consumer<? super T> consumer)

If a value is present, invoke the specified consumer with the value, otherwise do nothing.

boolean isPresent()

Return true if there is a value present, otherwise false.

<U> Optional<U> map(Function<? super T, ? extends U> mapper)

If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Optional describing the result.

static <T> Optional<T> of(T value)

Returns an Optional with the specified present non-null value.

static <T> Optional<T> ofNullable(T value)

Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.

T orElse(T other)

Return the value if present, otherwise return other.

T orElseGet(Supplier<? extends T> other)

Return the value if present, otherwise invoke other and return the result of that invocation.

<X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier)

Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.

String toString()

Returns a non-empty string representation of this Optional suitable for debugging.

Inherited methods

From class java.lang.Object

Public methods

empty

added in API level 24
Optional<T> empty ()

Returns an empty Optional instance. No value is present for this Optional.

API Note:
  • Though it may be tempting to do so, avoid testing if an object is empty by comparing with == against instances returned by Option.empty(). There is no guarantee that it is a singleton. Instead, use isPresent().
Returns
Optional<T> an empty Optional

equals

added in API level 24
boolean equals (Object obj)

Indicates whether some other object is "equal to" this Optional. The other object is considered equal if:

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

Parameters
obj Object: an object to be tested for equality

Returns
boolean {code true} if the other object is "equal to" this object otherwise false

filter

added in API level 24
Optional<T> filter (Predicate<? super T> predicate)

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

Parameters
predicate Predicate: a predicate to apply to the value, if present

Returns
Optional<T> an Optional describing the value of this Optional if a value is present and the value matches the given predicate, otherwise an empty Optional

Throws
NullPointerException if the predicate is null

flatMap

added in API level 24
Optional<U> flatMap (Function<? super T, Optional<U>> mapper)

If a value is present, apply the provided Optional-bearing mapping function to it, return that result, otherwise return an empty Optional. This method is similar to map(Function), but the provided mapper is one whose result is already an Optional, and if invoked, flatMap does not wrap it with an additional Optional.

Parameters
mapper Function: a mapping function to apply to the value, if present the mapping function

Returns
Optional<U> the result of applying an Optional-bearing mapping function to the value of this Optional, if a value is present, otherwise an empty Optional

Throws
NullPointerException if the mapping function is null or returns a null result

get

added in API level 24
T get ()

If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.

Returns
T the non-null value held by this Optional

Throws
NoSuchElementException if there is no value present

See also:

hashCode

added in API level 24
int hashCode ()

Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.

Returns
int hash code value of the present value or 0 if no value is present

ifPresent

added in API level 24
void ifPresent (Consumer<? super T> consumer)

If a value is present, invoke the specified consumer with the value, otherwise do nothing.

Parameters
consumer Consumer: block to be executed if a value is present

Throws
NullPointerException if value is present and consumer is null

isPresent

added in API level 24
boolean isPresent ()

Return true if there is a value present, otherwise false.

Returns
boolean true if there is a value present, otherwise false

map

added in API level 24
Optional<U> map (Function<? super T, ? extends U> mapper)

If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Optional describing the result. Otherwise return 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 file names, selects one that has not yet been processed, and then opens that file, returning an Optional<FileInputStream>:
    Optional<FileInputStream> fis =
             names.stream().filter(name -> !isProcessedYet(name))
                           .findFirst()
                           .map(name -> new FileInputStream(name));
     
    Here, findFirst returns an Optional<String>, and then map returns an Optional<FileInputStream> for the desired file if one exists.
Parameters
mapper Function: a mapping function to apply to the value, if present

Returns
Optional<U> an Optional describing the result of applying a mapping function to the value of this Optional, if a value is present, otherwise an empty Optional

Throws
NullPointerException if the mapping function is null

of

added in API level 24
Optional<T> of (T value)

Returns an Optional with the specified present non-null value.

Parameters
value T: the value to be present, which must be non-null

Returns
Optional<T> an Optional with the value present

Throws
NullPointerException if value is null

ofNullable

added in API level 24
Optional<T> ofNullable (T value)

Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.

Parameters
value T: the possibly-null value to describe

Returns
Optional<T> an Optional with a present value if the specified value is non-null, otherwise an empty Optional

orElse

added in API level 24
T orElse (T other)

Return the value if present, otherwise return other.

Parameters
other T: the value to be returned if there is no value present, may be null

Returns
T the value, if present, otherwise other

orElseGet

added in API level 24
T orElseGet (Supplier<? extends T> other)

Return the value if present, otherwise invoke other and return the result of that invocation.

Parameters
other Supplier: a Supplier whose result is returned if no value is present

Returns
T the value if present otherwise the result of other.get()

Throws
NullPointerException if value is not present and other is null

orElseThrow

added in API level 24
T orElseThrow (Supplier<? extends X> exceptionSupplier)

Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.

API Note:
  • A method reference to the exception constructor with an empty argument list can be used as the supplier. For example, IllegalStateException::new
Parameters
exceptionSupplier Supplier: The supplier which will return the exception to be thrown

Returns
T the present value

Throws
if there is no value present
NullPointerException if no value is present and exceptionSupplier is null
Throwable

toString

added in API level 24
String 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.

Implementation Requirements:
  • If a value is present the result must include its string representation in the result. Empty and present Optionals must be unambiguously differentiable.
Returns
String the string representation of this instance

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