Package Summary Overview Summary

### class:Optional [NONE]
- 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:empty() [NONE]
- #### 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`

### method:of(T) [NONE]
- #### 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`

### method:ofNullable(T) [NONE]
- #### 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`

### method:get() [NONE]
- #### 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

### method:isPresent() [NONE]
- #### isPresent
      public boolean isPresent()
If a value is present, returns `true`, otherwise `false`. Returns: `true` if a value is present, otherwise `false`

### method:isEmpty() [NONE]
- #### 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

### method:ifPresent(java.util.function.Consumer) [NONE]
- #### 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`

### method:ifPresentOrElse(java.util.function.Consumer,java.lang.Runnable) [NONE]
- #### 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

### method:filter(java.util.function.Predicate) [NONE]
- #### 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 a 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`

### method:map(java.util.function.Function) [NONE]
- #### 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`

### method:flatMap(java.util.function.Function) [NONE]
- #### 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

### method:or(java.util.function.Supplier) [NONE]
- #### 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

### method:stream() [NONE]
- #### 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

### method:orElse(T) [NONE]
- #### 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`

### method:orElseGet(java.util.function.Supplier) [NONE]
- #### 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 no value is present and the supplying function is `null`

### method:orElseThrow() [NONE]
- #### 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

### method:orElseThrow(java.util.function.Supplier) [NONE]
- #### 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`

### method:equals(java.lang.Object) [NONE]
- #### 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` See Also: `Object.hashCode()`, `HashMap`

### method:hashCode() [NONE]
- #### 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 See Also: `Object.equals(java.lang.Object)`, `System.identityHashCode(java.lang.Object)`

### method:toString() [NONE]
- #### 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. Overrides: `toString` in class `Object` Implementation Requirements: If a value is present the result must include its string representation in the result. Empty and present `Optional`s must be unambiguously differentiable. Returns: the string representation of this instance