Added in API level 24

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() 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; 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.

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, returns an Optional describing the value, otherwise returns an empty Optional.

<U> Optional<U> 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.

T get()

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

int hashCode()

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

void ifPresent(Consumer<? super T> action)

If a value is present, performs the given action with the value, otherwise does nothing.

void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)

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

boolean isEmpty()

If a value is not present, returns true, otherwise false.

boolean isPresent()

If a value is present, returns true, otherwise false.

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

Returns an Optional describing the given non-null value.

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

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

Optional<T> 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.

T orElse(T other)

If a value is present, returns the value, otherwise returns other.

T orElseGet(Supplier<? extends T> supplier)

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

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

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

T orElseThrow()

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

Stream<T> stream()

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

String toString()

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

Inherited methods

Public methods

empty

Added in API level 24
public static 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 == or != against instances returned by Optional.empty(). There is no guarantee that it is a singleton. Instead, use isEmpty() or isPresent().
Returns
Optional<T> an empty Optional

equals

Added in API level 24
public 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 true if the other object is "equal to" this object otherwise false

filter

Added in API level 24
public Optional<T> 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.

Parameters
predicate Predicate: the predicate to apply to a 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
public Optional<U> 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.

This method is similar to map(java.util.function.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.

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

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
public T get ()

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

API Note:
Returns
T the non-null value described by this Optional

Throws
NoSuchElementException if no value is present

hashCode

Added in API level 24
public int hashCode ()

Returns the hash code of the value, if present, otherwise 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
public void ifPresent (Consumer<? super T> action)

If a value is present, performs the given action with the value, otherwise does nothing.

Parameters
action Consumer: the action to be performed, if a value is present

Throws
NullPointerException if value is present and the given action is null

ifPresentOrElse

Added in API level 33
public void ifPresentOrElse (Consumer<? super T> action, 
                Runnable emptyAction)

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

Parameters
action Consumer: the action to be performed, if a value is present

emptyAction Runnable: the empty-based action to be performed, if no value is present

Throws
NullPointerException if a value is present and the given action is null, or no value is present and the given empty-based action is null.

isEmpty

Added in API level 33
public boolean isEmpty ()

If a value is not present, returns true, otherwise false.

Returns
boolean true if a value is not present, otherwise false

isPresent

Added in API level 24
public boolean isPresent ()

If a value is present, returns true, otherwise false.

Returns
boolean true if a value is present, otherwise false

map

Added in API level 24
public Optional<U> 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.

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<Path>:
    Optional<Path> p =
             uris.stream().filter(uri -> !isProcessedYet(uri))
                           .findFirst()
                           .map(Paths::get);
     
    Here, findFirst returns an Optional<URI>, and then map returns an Optional<Path> for the desired URI if one exists.
Parameters
mapper Function: the mapping function to apply to a 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
public static Optional<T> of (T value)

Returns an Optional describing the given non-null value.

Parameters
value T: the value to describe, 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
public static Optional<T> ofNullable (T value)

Returns an Optional describing the given 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

or

Added in API level 33
public Optional<T> 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.

Parameters
supplier Supplier: the supplying function that produces an Optional to be returned

Returns
Optional<T> returns an Optional describing the value of this Optional, if a value is present, otherwise an Optional produced by the supplying function.

Throws
NullPointerException if the supplying function is null or produces a null result

orElse

Added in API level 24
public T orElse (T other)

If a value is present, returns the value, otherwise returns other.

Parameters
other T: the value to be returned, if no value is present. May be null.

Returns
T the value, if present, otherwise other

orElseGet

Added in API level 24
public T orElseGet (Supplier<? extends T> supplier)

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

Parameters
supplier Supplier: the supplying function that produces a value to be returned

Returns
T the value, if present, otherwise the result produced by the supplying function

Throws
NullPointerException if no value is present and the supplying function is null

orElseThrow

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

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

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 supplying function that produces an exception to be thrown

Returns
T the value, if present

Throws
if no value is present
NullPointerException if no value is present and the exception supplying function is null
Throwable

orElseThrow

Added in API level 33
public T orElseThrow ()

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

Returns
T the non-null value described by this Optional

Throws
NoSuchElementException if no value is present

stream

Added in API level 33
public Stream<T> 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<Optional<T>> os = ..
         Stream<T> s = os.flatMap(Optional::stream)
     
Returns
Stream<T> the optional value as a Stream

toString

Added in API level 24
public 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