Added in API level 24

Optional

class Optional<T : Any!>

kotlin.Any
↳	java.util.Optional

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 Optional<T>	`empty()` Returns an empty `Optional` instance.
Boolean	`equals(other: Any?)` Indicates whether some other object is "equal to" this `Optional`.
Optional<T>!	`filter(predicate: Predicate<in T>!)` If a value is present, and the value matches the given predicate, returns an `Optional` describing the value, otherwise returns an empty `Optional`.
Optional<U>!	`flatMap(mapper: Function<in T, out Optional<out U>!>!)` 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.
Unit	`ifPresent(action: Consumer<in T>)` If a value is present, performs the given action with the value, otherwise does nothing.
Unit	`ifPresentOrElse(action: Consumer<in T>!, emptyAction: Runnable!)` 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`.
Optional<U>!	`map(mapper: Function<in T, out U>!)` If a value is present, returns an `Optional` describing (as if by `ofNullable`) the result of applying the given mapping function to the value, otherwise returns an empty `Optional`.
static Optional<T>	`of(value: T)` Returns an `Optional` describing the given non-`null` value.
static Optional<T>	`ofNullable(value: T?)` Returns an `Optional` describing the given value, if non-`null`, otherwise returns an empty `Optional`.
Optional<T>!	`or(supplier: Supplier<out Optional<out T>!>!)` If a value is present, returns an `Optional` describing the value, otherwise returns an `Optional` produced by the supplying function.
T	`orElse(other: T)` If a value is present, returns the value, otherwise returns `other`.
T	`orElseGet(supplier: Supplier<out T>!)` If a value is present, returns the value, otherwise returns the result produced by the supplying function.
T	`orElseThrow()` If a value is present, returns the value, otherwise throws `NoSuchElementException`.
T	`orElseThrow(exceptionSupplier: Supplier<out X>!)` If a value is present, returns the value, otherwise throws an exception produced by the exception supplying function.
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.

Public methods

empty

Added in API level 24

static fun <T : Any!> empty(): Optional<T>

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

Parameters
`<T>`	The type of the non-existent value

Return
`Optional<T>`	an empty `Optional`

equals

Added in API level 24

fun equals(other: Any?): Boolean

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`	an object to be tested for equality

Return
`Boolean`	`true` if the other object is "equal to" this object otherwise `false`

filter

Added in API level 24

fun filter(predicate: Predicate<in T>!): Optional<T>!

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<in T>!: the predicate to apply to a value, if present

Return
`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`

Exceptions
`java.lang.NullPointerException`	if the predicate is `null`

flatMap

Added in API level 24

fun <U : Any!> flatMap(mapper: Function<in T, out Optional<out U>!>!): Optional<U>!

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
`<U>`	The type of value of the `Optional` returned by the mapping function
`mapper`	Function<in T, out Optional<out U>!>!: the mapping function to apply to a value, if present

Return
`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`

Exceptions
`java.lang.NullPointerException`	if the mapping function is `null` or returns a `null` result

get

Added in API level 24

fun get(): T

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

Return
`T`	the non-`null` value described by this `Optional`

Exceptions
`java.util.NoSuchElementException`	if no value is present

hashCode

Added in API level 24

fun hashCode(): Int

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

Return
`Int`	hash code value of the present value or `0` if no value is present

ifPresent

Added in API level 24

fun ifPresent(action: Consumer<in T>): Unit

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

Parameters
`action`	Consumer<in T>: the action to be performed, if a value is present

Exceptions
`java.lang.NullPointerException`	if value is present and the given action is `null`

ifPresentOrElse

Added in API level 33

fun ifPresentOrElse(
    action: Consumer<in T>!, 
    emptyAction: Runnable!
): Unit

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

Parameters
`action`	Consumer<in T>!: the action to be performed, if a value is present
`emptyAction`	Runnable!: the empty-based action to be performed, if no value is present

Exceptions
`java.lang.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

fun isEmpty(): Boolean

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

Return
`Boolean`	`true` if a value is not present, otherwise `false`

isPresent

Added in API level 24

fun isPresent(): Boolean

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

Return
`Boolean`	`true` if a value is present, otherwise `false`

map

Added in API level 24

fun <U : Any!> map(mapper: Function<in T, out U>!): Optional<U>!

If a value is present, returns an Optional describing (as if by ofNullable) 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.

Parameters
`mapper`	Function<in T, out U>!: the mapping function to apply to a value, if present
`<U>`	The type of the value returned from the mapping function

Return
`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`

Exceptions
`java.lang.NullPointerException`	if the mapping function is `null`

of

Added in API level 24

static fun <T : Any!> of(value: T): Optional<T>

Returns an Optional describing the given non-null value.

Parameters
`value`	T: the value to describe, which must be non-`null`
`<T>`	the type of the value

Return
`Optional<T>`	an `Optional` with the value present

Exceptions
`java.lang.NullPointerException`	if value is `null`

ofNullable

Added in API level 24

static fun <T : Any!> ofNullable(value: T?): Optional<T>

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

Parameters
`value`	T?: the possibly-`null` value to describe
`<T>`	the type of the value

Return
`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

fun or(supplier: Supplier<out Optional<out T>!>!): Optional<T>!

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

Parameters
`supplier`	Supplier<out Optional<out T>!>!: the supplying function that produces an `Optional` to be returned

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

Exceptions
`java.lang.NullPointerException`	if the supplying function is `null` or produces a `null` result

orElse

Added in API level 24

fun orElse(other: T): T

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`.

Return
`T`	the value, if present, otherwise `other`

orElseGet

Added in API level 24

fun orElseGet(supplier: Supplier<out T>!): T

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

Parameters
`supplier`	Supplier<out T>!: the supplying function that produces a value to be returned

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

Exceptions
`java.lang.NullPointerException`	if no value is present and the supplying function is `null`

orElseThrow

Added in API level 33

fun orElseThrow(): T

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

Return
`T`	the non-`null` value described by this `Optional`

Exceptions
`java.util.NoSuchElementException`	if no value is present

orElseThrow

Added in API level 24

fun <X : Throwable!> orElseThrow(exceptionSupplier: Supplier<out X>!): T

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

Parameters
`<X>`	Type of the exception to be thrown
`exceptionSupplier`	Supplier<out X>!: the supplying function that produces an exception to be thrown

Return
`T`	the value, if present

Exceptions
`X`	if no value is present
`java.lang.NullPointerException`	if no value is present and the exception supplying function is `null`

stream

Added in API level 33

fun stream(): Stream<T>!

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

Return
`Stream<T>!`	the optional value as a `Stream`

toString

Added in API level 24

fun toString(): String

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.

Return
`String`	the string representation of this instance