Optional
public
final
class
Optional
extends Object
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 |
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static
<T>
Optional<T>
|
empty()
Returns an empty Optional instance.
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boolean
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equals(Object obj)
Indicates whether some other object is "equal to" this Optional.
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Optional<T>
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filter(Predicate<? super T> predicate)
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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<U>
Optional<U>
|
flatMap(Function<? super T, Optional<U>> mapper)
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
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get()
If a value is present in this Optional, returns the value,
otherwise throws NoSuchElementException.
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int
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hashCode()
Returns the hash code value of the present value, if any, or 0 (zero) if
no value is present.
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void
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ifPresent(Consumer<? super T> consumer)
If a value is present, invoke the specified consumer with the value,
otherwise do nothing.
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boolean
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isPresent()
Return true if there is a value present, otherwise false.
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<U>
Optional<U>
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map(Function<? super T, ? extends U> mapper)
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
<T>
Optional<T>
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of(T value)
Returns an Optional with the specified present non-null value.
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static
<T>
Optional<T>
|
ofNullable(T value)
Returns an Optional describing the specified value, if non-null,
otherwise returns an empty Optional.
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T
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orElse(T other)
Return the value if present, otherwise return other.
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T
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orElseGet(Supplier<? extends T> other)
Return the value if present, otherwise invoke other and return
the result of that invocation.
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<X extends Throwable>
T
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orElseThrow(Supplier<? extends X> exceptionSupplier)
Return the contained value, if present, otherwise throw an exception
to be created by the provided supplier.
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String
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toString()
Returns a non-empty string representation of this Optional suitable for
debugging.
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Inherited methods |
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 From
class
java.lang.Object
Object
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clone()
Creates and returns a copy of this object.
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boolean
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equals(Object obj)
Indicates whether some other object is "equal to" this one.
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void
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finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
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final
Class<?>
|
getClass()
Returns the runtime class of this Object.
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int
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hashCode()
Returns a hash code value for the object.
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final
void
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notify()
Wakes up a single thread that is waiting on this object's
monitor.
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final
void
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notifyAll()
Wakes up all threads that are waiting on this object's monitor.
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String
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toString()
Returns a string representation of the object.
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final
void
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wait(long millis, int nanos)
Causes the current thread to wait until another thread invokes the
notify() method or the
notifyAll() method for this object, or
some other thread interrupts the current thread, or a certain
amount of real time has elapsed.
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final
void
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wait(long millis)
Causes the current thread to wait until either another thread invokes the
notify() method or the
notifyAll() method for this object, or a
specified amount of time has elapsed.
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final
void
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wait()
Causes the current thread to wait until another thread invokes the
notify() method or the
notifyAll() method for this object.
|
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Public methods
empty
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
== against instances returned by
Option.empty(). There is no guarantee that it is a singleton.
Instead, use isPresent().
equals
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 |
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obj |
Object:
an object to be tested for equality |
| Returns |
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boolean |
{code true} if the other object is "equal to" this object
otherwise false
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filter
Optional<T> filter (Predicate<? super T> predicate)
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:
a predicate to apply to the 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 |
flatMap
Optional<U> flatMap (Function<? super T, Optional<U>> mapper)
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(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 |
|---|
mapper |
Function:
a mapping function to apply to the value, if present
the mapping function |
| Returns |
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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 |
get
T get ()
If a value is present in this Optional, returns the value,
otherwise throws NoSuchElementException.
| Returns |
|---|
T |
the non-null value held by this Optional |
hashCode
int hashCode ()
Returns the hash code value of the present value, if any, or 0 (zero) if
no value is present.
| Returns |
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int |
hash code value of the present value or 0 if no value is present
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ifPresent
void ifPresent (Consumer<? super T> consumer)
If a value is present, invoke the specified consumer with the value,
otherwise do nothing.
| Parameters |
|---|
consumer |
Consumer:
block to be executed if a value is present |
isPresent
boolean isPresent ()
Return true if there is a value present, otherwise false.
| Returns |
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boolean |
true if there is a value present, otherwise false
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map
Optional<U> map (Function<? super T, ? extends U> mapper)
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 |
|---|
mapper |
Function:
a mapping function to apply to the value, if present |
| Returns |
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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 |
of
Optional<T> of (T value)
Returns an Optional with the specified present non-null value.
| Parameters |
|---|
value |
T:
the value to be present, which must be non-null |
| Returns |
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Optional<T> |
an Optional with the value present |
ofNullable
Optional<T> ofNullable (T value)
Returns an Optional describing the specified value, if non-null,
otherwise returns an empty Optional.
| Parameters |
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value |
T:
the possibly-null value to describe |
| Returns |
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Optional<T> |
an Optional with a present value if the specified value
is non-null, otherwise an empty Optional
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orElse
T orElse (T other)
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 |
| Returns |
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T |
the value, if present, otherwise other
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orElseGet
T orElseGet (Supplier<? extends T> other)
Return the value if present, otherwise invoke other and return
the result of that invocation.
| Parameters |
|---|
other |
Supplier:
a Supplier whose result is returned if no value
is present |
| Returns |
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T |
the value if present otherwise the result of other.get() |
orElseThrow
T orElseThrow (Supplier<? extends X> exceptionSupplier)
Return the contained value, if present, otherwise throw an exception
to be created by the provided supplier.
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 |
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exceptionSupplier |
Supplier:
The supplier which will return the exception to
be thrown |
| Returns |
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T |
the present value |
toString
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 |
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String |
the string representation of this instance
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Developers