# Class OptionalDouble

java.lang.Object
java.util.OptionalDouble

public final class OptionalDouble extends Object
A container object which may or may not contain a `double` 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; programmers should treat instances that are equal as interchangeable and should not use instances for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail.

API Note:
  `OptionalDouble` is primarily intended for use as a method return type where there is a clear need to represent "no result." A variable whose type is `OptionalDouble` should never itself be `null`; it should always point to an `OptionalDouble` instance.
Since:
  1.8

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static OptionalDouble`
  `empty()`
  Returns an empty `OptionalDouble` instance.
  `boolean`
  `equals(Object obj)`
  Indicates whether some other object is "equal to" this `OptionalDouble`.
  `double`
  `getAsDouble()`
  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(DoubleConsumer action)`
  If a value is present, performs the given action with the value, otherwise does nothing.
  `void`
  `ifPresentOrElse(DoubleConsumer 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`.
  `static OptionalDouble`
  `of(double value)`
  Returns an `OptionalDouble` describing the given value.
  `double`
  `orElse(double other)`
  If a value is present, returns the value, otherwise returns `other`.
  `double`
  `orElseGet(DoubleSupplier supplier)`
  If a value is present, returns the value, otherwise returns the result produced by the supplying function.
  `double`
  `orElseThrow()`
  If a value is present, returns the value, otherwise throws `NoSuchElementException`.
  `<X extends Throwable>
  double`
  `orElseThrow(Supplier<? extends X> exceptionSupplier)`
  If a value is present, returns the value, otherwise throws an exception produced by the exception supplying function.
  `DoubleStream`
  `stream()`
  If a value is present, returns a sequential `DoubleStream` containing only that value, otherwise returns an empty `DoubleStream`.
  `String`
  `toString()`
  Returns a non-empty string representation of this `OptionalDouble` suitable for debugging.

  ### Methods declared in class Object

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

- ## Method Details

  - ### empty

    public static OptionalDouble empty()
    Returns an empty `OptionalDouble` instance. No value is present for this `OptionalDouble`.
    API Note:
      Though it may be tempting to do so, avoid testing if an object is empty by comparing with `==` or `!=` against instances returned by `OptionalDouble.empty()`. There is no guarantee that it is a singleton. Instead, use `isEmpty()` or `isPresent()`.
    Returns:
      an empty `OptionalDouble`.

  - ### of

    public static OptionalDouble of(double value)
    Returns an `OptionalDouble` describing the given value.
    Parameters:
      `value` - the value to describe
    Returns:
      an `OptionalDouble` with the value present

  - ### getAsDouble

    public double getAsDouble()
    If a value is present, returns the value, otherwise throws `NoSuchElementException`.
    API Note:
      The preferred alternative to this method is `orElseThrow()`.
    Returns:
      the value described by this `OptionalDouble`
    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(DoubleConsumer 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(DoubleConsumer 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

  - ### stream

    public DoubleStream stream()
    If a value is present, returns a sequential `DoubleStream` containing only that value, otherwise returns an empty `DoubleStream`.
    API Note:
      This method can be used to transform a `Stream` of optional doubles to a `DoubleStream` of present doubles:

              Stream<OptionalDouble> os = ..
              DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)

    Returns:
      the optional value as a `DoubleStream`
    Since:
      9

  - ### orElse

    public double orElse(double other)
    If a value is present, returns the value, otherwise returns `other`.
    Parameters:
      `other` - the value to be returned, if no value is present
    Returns:
      the value, if present, otherwise `other`

  - ### orElseGet

    public double orElseGet(DoubleSupplier 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`

  - ### orElseThrow

    public double orElseThrow()
    If a value is present, returns the value, otherwise throws `NoSuchElementException`.
    Returns:
      the value described by this `OptionalDouble`
    Throws:
      `NoSuchElementException` - if no value is present
    Since:
      10

  - ### orElseThrow

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

  - ### equals

    public boolean equals(Object obj)
    Indicates whether some other object is "equal to" this `OptionalDouble`. The other object is considered equal if:
    - it is also an `OptionalDouble` and;
    - both instances have no value present or;
    - the present values are "equal to" each other via `Double.compare() == 0`.
    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`

  - ### 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(Object)`

  - ### toString

    public String toString()
    Returns a non-empty string representation of this `OptionalDouble` 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 `OptionalDouble`s must be unambiguously differentiable.
    Returns:
      the string representation of this instance