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>

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

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

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

Boolean

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

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>!

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

String

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