Optional (net.sourceforge.streamsupport:streamsupport 1.7.0 API)

java.lang.Object
- java8.util.Optional<T>

Type Parameters:

T - the type of value
```
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() 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; 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.
API Note:
Optional is primarily intended for use as a method return type where there is a clear need to represent "no result", and where using null is likely to cause errors. A variable whose type is Optional should never itself be null; it should always point to an Optional instance.

Since:

1.8

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`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, returns an `Optional` describing the value, otherwise returns an empty `Optional`.
`<U> Optional<U>`	`flatMap(Function<? super T,? extends Optional<? extends U>> mapper)` 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`	`hashCode()` Returns the hash code of the value, if present, otherwise `0` (zero) if no value is present.
`void`	`ifPresent(Consumer<? super T> action)` If a value is present, performs the given action with the value, otherwise does nothing.
`void`	`ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)` If a value is present, performs the given action with the value, otherwise performs the given empty-based action.
`boolean`	`isEmpty()` If a value is not present, returns `true`, otherwise `false`.
`boolean`	`isPresent()` If a value is present, returns `true`, otherwise `false`.
`<U> Optional<U>`	`map(Function<? super T,? extends U> mapper)` If a value is present, returns an `Optional` describing (as if by `ofNullable(T)`) the result of applying the given mapping function to the value, otherwise returns an empty `Optional`.
`static <T> Optional<T>`	`of(T value)` Returns an `Optional` describing the given non-`null` value.
`static <T> Optional<T>`	`ofNullable(T value)` Returns an `Optional` describing the given value, if non-`null`, otherwise returns an empty `Optional`.
`Optional<T>`	`or(Supplier<? extends Optional<? extends T>> supplier)` If a value is present, returns an `Optional` describing the value, otherwise returns an `Optional` produced by the supplying function.
`T`	`orElse(T other)` If a value is present, returns the value, otherwise returns `other`.
`T`	`orElseGet(Supplier<? extends T> supplier)` If a value is present, returns the value, otherwise returns the result produced by the supplying function.
`T`	`orElseThrow()` If a value is present, returns the value, otherwise throws `NoSuchElementException`.
`<X extends Throwable> T`	`orElseThrow(Supplier<? extends X> exceptionSupplier)` If a value is present, returns the value, otherwise throws an exception produced by the exception supplying function.
`Stream<T>`	`stream()` If a value is present, returns a sequential `Stream` containing only that value, otherwise returns an empty `Stream`.
`String`	`toString()` Returns a non-empty string representation of this `Optional` suitable for debugging.

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Method Detail
  - empty
```
public static <T> 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 Optional.empty(). There is no guarantee that it is a singleton. Instead, use isPresent().
    
    Type Parameters:
    
    T - The type of the non-existent value
    
    Returns:
    
    an empty Optional
  - of
```
public static <T> Optional<T> of(T value)
```
    Returns an Optional describing the given non-null value.
    
    Type Parameters:
    
    T - the type of the value
    
    Parameters:
    
    value - the value to describe, which must be non-null
    
    Returns:
    
    an Optional with the value present
    
    Throws:
    
    NullPointerException - if value is null
  - ofNullable
```
public static <T> Optional<T> ofNullable(T value)
```
    Returns an Optional describing the given value, if non-null, otherwise returns an empty Optional.
    
    Type Parameters:
    
    T - the type of the value
    
    Parameters:
    
    value - the possibly-null value to describe
    
    Returns:
    
    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, returns the value, otherwise throws NoSuchElementException.
    API Note:
    The preferred alternative to this method is orElseThrow().
    
    Returns:
    
    the non-null value described by this Optional
    
    Throws:
    
    NoSuchElementException - if no value is present
  - isPresent
```
public boolean isPresent()
```
    If a value is present, returns true, otherwise false.
    
    Returns:
    
    true if a value is present, otherwise false
  - isEmpty
```
public boolean isEmpty()
```
    If a value is not present, returns true, otherwise false.
    
    Returns:
    
    true if a value is not present, otherwise false
    
    Since:
    
    11
  - ifPresent
```
public void ifPresent(Consumer<? super T> action)
```
    If a value is present, performs the given action with the value, otherwise does nothing.
    
    Parameters:
    
    action - the action to be performed, if a value is present
    
    Throws:
    
    NullPointerException - if value is present and the given action is null
  - ifPresentOrElse
```
public void ifPresentOrElse(Consumer<? super T> action,
                            Runnable emptyAction)
```
    If a value is present, performs the given action with the value, otherwise performs the given empty-based action.
    
    Parameters:
    
    action - the action to be performed, if a value is present
    
    emptyAction - the empty-based action to be performed, if no value is present
    
    Throws:
    
    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.
    
    Since:
    
    9
  - filter
```
public Optional<T> filter(Predicate<? super T> predicate)
```
    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 - the predicate to apply to the value, if present
    
    Returns:
    
    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
  - map
```
public <U> Optional<U> map(Function<? super T,? extends U> mapper)
```
    If a value is present, returns an Optional describing (as if by ofNullable(T)) 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.
    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 URIs, selects one that has not yet been processed, and creates a path from that URI, returning an Optional<Path>:
```
     Optional<Path> p =
         uris.stream().filter(uri -> !isProcessedYet(uri))
                       .findFirst()
                       .map(Paths::get);
 
```
    Here, findFirst returns an Optional<URI>, and then map returns an Optional<Path> for the desired URI if one exists.
    Type Parameters:
    
    U - The type of the value returned from the mapping function
    
    Parameters:
    
    mapper - the mapping function to apply to a value, if present
    
    Returns:
    
    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
  - flatMap
```
public <U> Optional<U> flatMap(Function<? super T,? extends Optional<? extends U>> mapper)
```
    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(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.
    
    Type Parameters:
    
    U - The type of value of the Optional returned by the mapping function
    
    Parameters:
    
    mapper - the mapping function to apply to a value, if present
    
    Returns:
    
    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
  - or
```
public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier)
```
    If a value is present, returns an Optional describing the value, otherwise returns an Optional produced by the supplying function.
    
    Parameters:
    
    supplier - the supplying function that produces an Optional to be returned
    
    Returns:
    
    returns an Optional describing the value of this Optional, if a value is present, otherwise an Optional produced by the supplying function.
    
    Throws:
    
    NullPointerException - if the supplying function is null or produces a null result
    
    Since:
    
    9
  - stream
```
public Stream<T> stream()
```
    If a value is present, returns a sequential Stream containing only that value, otherwise returns an empty Stream.
    API Note:
    This method can be used to transform a Stream of optional elements to a Stream of present value elements:
```
     Stream<Optional<T>> os = ..
     Stream<T> s = os.flatMap(Optional::stream)
 
```
    Returns:
    
    the optional value as a Stream
    
    Since:
    
    9
  - orElse
```
public T orElse(T other)
```
    If a value is present, returns the value, otherwise returns other.
    
    Parameters:
    
    other - the value to be returned, if no value is present. May be null
    
    Returns:
    
    the value, if present, otherwise other
  - orElseGet
```
public T orElseGet(Supplier<? extends T> supplier)
```
    If a value is present, returns the value, otherwise returns the result produced by the supplying function.
    
    Parameters:
    
    supplier - the supplying function that produces a value to be returned
    
    Returns:
    
    the value, if present, otherwise the result produced by the supplying function
    
    Throws:
    
    NullPointerException - if value is not present and the supplying function is null
  - orElseThrow
```
public T orElseThrow()
```
    If a value is present, returns the value, otherwise throws NoSuchElementException.
    
    Returns:
    
    the non-null value described by this Optional
    
    Throws:
    
    NoSuchElementException - if no value is present
    
    Since:
    
    10
  - orElseThrow
```
public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier)
                                    throws X extends Throwable
```
    If a value is present, returns the value, otherwise throws an exception produced by the exception supplying function.
    API Note:
    A method reference to the exception constructor with an empty argument list can be used as the supplier. For example, IllegalStateException::new
    
    Type Parameters:
    
    X - Type of the exception to be thrown
    
    Parameters:
    
    exceptionSupplier - the supplying function that produces an exception to be thrown
    
    Returns:
    
    the value, if present
    
    Throws:
    
    X - if no value is present
    
    NullPointerException - if no value is present and the exception supplying function 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().
    Overrides:
    
    equals in class Object
    
    Parameters:
    
    obj - an object to be tested for equality
    
    Returns:
    
    true if the other object is "equal to" this object otherwise false
  - hashCode
```
public int hashCode()
```
    Returns the hash code of the value, if present, otherwise 0 (zero) if no value is present.
    
    Overrides:
    
    hashCode in class Object
    
    Returns:
    
    hash code value of the present value or 0 if no value is present
  - 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.
    
    Overrides:
    
    toString in class Object
    
    Returns:
    
    the string representation of this instance

Class Optional<T>

Method Summary

Methods inherited from class java.lang.Object

Method Detail

empty

of

ofNullable

get

isPresent

isEmpty

ifPresent

ifPresentOrElse

filter

map

flatMap

or

stream

orElse

orElseGet

orElseThrow

orElseThrow

equals

hashCode

toString