compact1, compact2, compact3
java.util

## 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()` will return `true` and `getAsDouble()` 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 `OptionalDouble` may have unpredictable results and should be avoided.

  Since:
    1.8

- - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    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 in this `OptionalDouble`, 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(DoubleConsumer consumer)` | Have the specified consumer accept the value if a value is present, otherwise do nothing.
    `boolean` | `isPresent()` | Return `true` if there is a value present, otherwise `false`.
    `static OptionalDouble` | `of(double value)` | Return an `OptionalDouble` with the specified value present.
    `double` | `orElse(double other)` | Return the value if present, otherwise return `other`.
    `double` | `orElseGet(DoubleSupplier other)` | Return the value if present, otherwise invoke `other` and return the result of that invocation.
    `<X extends Throwable> double` | `orElseThrow(Supplier<X> exceptionSupplier)` | Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
    `String` | `toString()` | Returns a string representation of the object.

    - ### Methods inherited from class java.lang.Object

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

- - ### Method Detail

    - #### 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 `==` against instances returned by `Option.empty()`. There is no guarantee that it is a singleton. Instead, use `isPresent()`.
      Returns:
        an empty `OptionalDouble`.

    - #### of

          public static OptionalDouble of(double value)

      Return an `OptionalDouble` with the specified value present.
      Parameters:
        `value` - the value to be present
      Returns:
        an `OptionalDouble` with the value present

    - #### getAsDouble

          public double getAsDouble()

      If a value is present in this `OptionalDouble`, returns the value, otherwise throws `NoSuchElementException`.
      Returns:
        the value held by this `OptionalDouble`
      Throws:
        `NoSuchElementException` - if there is no value present
      See Also:
        `isPresent()`

    - #### isPresent

          public boolean isPresent()

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

    - #### ifPresent

          public void ifPresent(DoubleConsumer consumer)

      Have the specified consumer accept the value if a value is present, otherwise do nothing.
      Parameters:
        `consumer` - block to be executed if a value is present
      Throws:
        `NullPointerException` - if value is present and `consumer` is null

    - #### orElse

          public double orElse(double other)

      Return the value if present, otherwise return `other`.
      Parameters:
        `other` - the value to be returned if there is no value present
      Returns:
        the value, if present, otherwise `other`

    - #### orElseGet

          public double orElseGet(DoubleSupplier other)

      Return the value if present, otherwise invoke `other` and return the result of that invocation.
      Parameters:
        `other` - a `DoubleSupplier` whose result is returned if no value is present
      Returns:
        the value if present otherwise the result of `other.getAsDouble()`
      Throws:
        `NullPointerException` - if value is not present and `other` is null

    - #### orElseThrow

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

      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`
      Type Parameters:
        `X` - Type of the exception to be thrown
      Parameters:
        `exceptionSupplier` - The supplier which will return the exception to be thrown
      Returns:
        the present value
      Throws:
        `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 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:
        {code 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 value of the present value, if any, or 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)`

    - #### toString

          public String toString()

      Returns a string representation of the object. In general, the `toString` method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

      The `toString` method for class `Object` returns a string consisting of the name of the class of which the object is an instance, the at-sign character ``@`', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

      >      getClass().getName() + '@' + Integer.toHexString(hashCode())

      Returns a non-empty string representation of this object 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 instances must be unambiguously differentiable.
      Returns:
        the string representation of this instance

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