Added in API level 24

Summary: Methods | Inherited Methods

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

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

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:

The preferred alternative to this method is orElseThrow().

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