Optional
class Optional<T : Any!>
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 Optional<T> |
Returns an empty Optional instance.
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| Boolean |
Indicates whether some other object is "equal to" this Optional.
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| Optional<T>! |
If a value is present, and the value matches the given predicate, return an Optional describing the value, otherwise return an empty Optional.
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| Optional<U>! |
If a value is present, apply the provided Optional-bearing mapping function to it, return that result, otherwise return an empty Optional.
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| T |
If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.
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| Int |
Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
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| Unit |
If a value is present, invoke the specified consumer with the value, otherwise do nothing.
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| Boolean |
Return true if there is a value present, otherwise false.
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| Optional<U>! |
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.
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| static Optional<T> |
Returns an Optional with the specified present non-null value.
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| static Optional<T> |
Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.
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| T |
Return the value if present, otherwise return other.
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| T |
Return the value if present, otherwise invoke other and return the result of that invocation.
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| T |
Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
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| String |
Returns a non-empty string representation of this Optional suitable for debugging.
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Public methods
empty
static fun <T : Any!> empty(): Optional<T>
Returns an empty Optional instance. No value is present for this Optional.
| Parameters |
<T> |
Type of the non-existent value |
equals
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 |
{code true} if the other object is "equal to" this object otherwise false |
filter
fun filter(predicate: Predicate<in T>!): Optional<T>!
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<in T>!: a predicate to apply to the 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
fun <U : Any!> flatMap(mapper: Function<in T, Optional<U>!>!): Optional<U>!
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(java.util.function.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 |
<U> |
The type parameter to the Optional returned by |
mapper |
Function<in T, Optional<U>!>!: a mapping function to apply to the value, if present the mapping function |
| 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
fun get(): T
If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.
| Return |
T |
the non-null value held by this Optional |
| Exceptions |
java.util.NoSuchElementException |
if there is no value present |
hashCode
fun hashCode(): Int
Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
| Return |
Int |
hash code value of the present value or 0 if no value is present |
ifPresent
fun ifPresent(consumer: Consumer<in T>): Unit
If a value is present, invoke the specified consumer with the value, otherwise do nothing.
| Parameters |
consumer |
Consumer<in T>: block to be executed if a value is present |
| Exceptions |
java.lang.NullPointerException |
if value is present and consumer is null |
isPresent
fun isPresent(): Boolean
Return true if there is a value present, otherwise false.
| Return |
Boolean |
true if there is a value present, otherwise false |
map
fun <U : Any!> map(mapper: Function<in T, out U>!): Optional<U>!
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.
| Parameters |
<U> |
The type of the result of the mapping function |
mapper |
Function<in T, out U>!: a mapping function to apply to the value, if present |
| 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
static fun <T : Any!> of(value: T): Optional<T>
Returns an Optional with the specified present non-null value.
| Parameters |
<T> |
the class of the value |
value |
T: the value to be present, which must be non-null |
| Return |
Optional<T> |
an Optional with the value present |
| Exceptions |
java.lang.NullPointerException |
if value is null |
ofNullable
static fun <T : Any!> ofNullable(value: T?): Optional<T>
Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.
| Parameters |
<T> |
the class of the value |
value |
T?: the possibly-null value to describe |
| Return |
Optional<T> |
an Optional with a present value if the specified value is non-null, otherwise an empty Optional |
orElse
fun orElse(other: T): T
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 |
| Return |
T |
the value, if present, otherwise other |
orElseGet
fun orElseGet(other: Supplier<out T>!): T
Return the value if present, otherwise invoke other and return the result of that invocation.
| Parameters |
other |
Supplier<out T>!: a Supplier whose result is returned if no value is present |
| Return |
T |
the value if present otherwise the result of other.get() |
| Exceptions |
java.lang.NullPointerException |
if value is not present and other is null |
orElseThrow
fun <X : Throwable!> orElseThrow(exceptionSupplier: Supplier<out X>!): T
Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
| Parameters |
<X> |
Type of the exception to be thrown |
exceptionSupplier |
Supplier<out X>!: The supplier which will return the exception to be thrown |
| Return |
T |
the present value |
| Exceptions |
X |
if there is no value present |
java.lang.NullPointerException |
if no value is present and exceptionSupplier is null |
toString
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 |
