程序包 java.util

类 Optional<T>

java.lang.Object

java.util.Optional<T>

public final class Optional<T>
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).

This is a value-based class; use of identity-sensitive operations (including reference equality (==), identity hash code, or synchronization) on instances of Optional may have unpredictable results and should be avoided.

从以下版本开始:

1.8

方法概要

限定符和类型	方法	说明
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, return an Optional describing the value, otherwise return an empty Optional.
<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.
T	get()	If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.
int	hashCode()	Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
void	ifPresent(Consumer<? super T> consumer)	If a value is present, invoke the specified consumer with the value, otherwise do nothing.
boolean	isPresent()	Return true if there is a value present, otherwise false.
<U> 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.
static <T> Optional<T>	of(T value)	Returns an Optional with the specified present non-null value.
static <T> Optional<T>	ofNullable(T value)	Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.
T	orElse(T other)	Return the value if present, otherwise return other.
T	orElseGet(Supplier<? extends T> other)	Return the value if present, otherwise invoke other and return the result of that invocation.
<X extends Throwable> T	orElseThrow(Supplier<? extends X> exceptionSupplier)	Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
String	toString()	Returns a non-empty string representation of this Optional suitable for debugging.

从类继承的方法 java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

方法详细资料

empty

public static <T> Optional<T> empty()

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

类型参数:

T - Type of the non-existent value

返回:

an empty Optional

of

public static <T> Optional<T> of(T value)

Returns an Optional with the specified present non-null value.

类型参数:

T - the class of the value

参数:

value - the value to be present, which must be non-null

返回:

an Optional with the value present

抛出:

NullPointerException - if value is null

ofNullable

public static <T> Optional<T> ofNullable(T value)

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

类型参数:

T - the class of the value

参数:

value - the possibly-null value to describe

返回:

an Optional with a present value if the specified value is non-null, otherwise an empty Optional

get

public T get()

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

返回:

the non-null value held by this Optional

抛出:

NoSuchElementException - if there is no value present

另请参阅:

isPresent()

isPresent

public boolean isPresent()

Return true if there is a value present, otherwise false.

返回:

true if there is a value present, otherwise false

ifPresent

public void ifPresent(Consumer<? super T> consumer)

If a value is present, invoke the specified consumer with the value, otherwise do nothing.

参数:

consumer - block to be executed if a value is present

抛出:

NullPointerException - if value is present and consumer is null

filter

public 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.

参数:

predicate - a predicate to apply to the value, if present

返回:

an Optional describing the value of this Optional if a value is present and the value matches the given predicate, otherwise an empty Optional

抛出:

NullPointerException - if the predicate is null

map

public <U> 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.

类型参数:

U - The type of the result of the mapping function

参数:

mapper - a mapping function to apply to the value, if present

返回:

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

抛出:

NullPointerException - if the mapping function is null

flatMap

public <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. 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.

类型参数:

U - The type parameter to the Optional returned by

参数:

mapper - a mapping function to apply to the value, if present the mapping function

返回:

the result of applying an Optional-bearing mapping function to the value of this Optional, if a value is present, otherwise an empty Optional

抛出:

NullPointerException - if the mapping function is null or returns a null result

orElse

public T orElse(T other)

Return the value if present, otherwise return other.

参数:

other - the value to be returned if there is no value present, may be null

返回:

the value, if present, otherwise other

orElseGet

public T orElseGet(Supplier<? extends T> other)

Return the value if present, otherwise invoke other and return the result of that invocation.

参数:

other - a Supplier whose result is returned if no value is present

返回:

the value if present otherwise the result of other.get()

抛出:

NullPointerException - if value is not present and other is null

orElseThrow

public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier)
                                    throws X extends Throwable

Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.

类型参数:

X - Type of the exception to be thrown

参数:

exceptionSupplier - The supplier which will return the exception to be thrown

返回:

the present value

抛出:

X - if there is no value present

NullPointerException - if no value is present and exceptionSupplier is null

X extends Throwable

equals

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().

覆盖:

equals 在类中 Object

参数:

obj - an object to be tested for equality

返回:

{code true} if the other object is "equal to" this object otherwise false

另请参阅:

Object.hashCode(), HashMap

hashCode

public int hashCode()

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

覆盖:

hashCode 在类中 Object

返回:

hash code value of the present value or 0 if no value is present

另请参阅:

Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

toString

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.

覆盖:

toString 在类中 Object

返回:

the string representation of this instance