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Summary: Methods | Inherited Methods

Optional

public final class Optional
extends Object

java.lang.Object
↳	java.util.Optional<T>

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 <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.

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeout, 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.
`final void`	`wait(long timeout)` 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.
`final void`	`wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

Public methods

empty

public static 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().

Returns
`Optional<T>`	an empty `Optional`

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().

Parameters
`obj`	`Object`: an object to be tested for equality

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

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.

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`

Throws
`NullPointerException`	if the predicate is null

flatMap

public 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.

Parameters
`mapper`	`Function`: a mapping function to apply to the value, if present the mapping function

Returns
`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`

Throws
`NullPointerException`	if the mapping function is null or returns a null result

get

public 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`

Throws
`NoSuchElementException`	if there is no value present

See also:

isPresent()

hashCode

public int hashCode ()

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

Returns
`int`	hash code value of the present value or 0 if no value is present

ifPresent

public 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

Throws
`NullPointerException`	if value is present and `consumer` is null

isPresent

public boolean isPresent ()

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

Returns
`boolean`	`true` if there is a value present, otherwise `false`

map

public 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.

API Note:

This method supports post-processing on optional values, without the need to explicitly check for a return status. For example, the following code traverses a stream of file names, selects one that has not yet been processed, and then opens that file, returning an Optional<FileInputStream>:
```
Optional<FileInputStream> fis =
         names.stream().filter(name -> !isProcessedYet(name))
                       .findFirst()
                       .map(name -> new FileInputStream(name));
 
```
Here, findFirst returns an Optional<String>, and then map returns an Optional<FileInputStream> for the desired file if one exists.

Parameters
`mapper`	`Function`: a mapping function to apply to the value, if present

Returns
`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`

Throws
`NullPointerException`	if the mapping function is null

of

public static 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
`Optional<T>`	an `Optional` with the value present

Throws
`NullPointerException`	if value is null

ofNullable

public static Optional<T> ofNullable (T value)

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

Parameters
`value`	`T`: the possibly-null value to describe

Returns
`Optional<T>`	an `Optional` with a present value if the specified value is non-null, otherwise an empty `Optional`

orElse

public 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
`T`	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.

Parameters
`other`	`Supplier`: a `Supplier` whose result is returned if no value is present

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

Throws
`NullPointerException`	if value is not present and `other` is null

orElseThrow

public 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
`exceptionSupplier`	`Supplier`: The supplier which will return the exception to be thrown

Returns
`T`	the present value

Throws
	if there is no value present
`NullPointerException`	if no value is present and `exceptionSupplier` is null
`Throwable`

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.

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
`String`	the string representation of this instance

Interfaces

Classes

Enums

Exceptions

Errors

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Results for

Optional

Summary

Public methods

Inherited methods

Public methods

empty

API Note:

equals

filter

flatMap

get

hashCode

ifPresent

isPresent

map

API Note:

of

ofNullable

orElse

orElseGet

orElseThrow

API Note:

toString

Implementation Requirements: