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	/*
	* Copyright (c) 2012, 2020, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	package java.util;

	import java.util.function.DoubleConsumer;
	import java.util.function.DoubleSupplier;
	import java.util.function.Supplier;
	import java.util.stream.DoubleStream;

	/**
	* A container object which may or may not contain a {@code double} value.
	* If a value is present, {@code isPresent()} returns {@code true}. If no
	* value is present, the object is considered <i>empty</i> and
	* {@code isPresent()} returns {@code false}.
	*
	* <p>Additional methods that depend on the presence or absence of a contained
	* value are provided, such as {@link #orElse(double) orElse()}
	* (returns a default value if no value is present) and
	* {@link #ifPresent(DoubleConsumer) ifPresent()} (performs
	* an action if a value is present).
	*
	* <p>This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
	* class; programmers should treat instances that are
	* {@linkplain #equals(Object) equal} as interchangeable and should not
	* use instances for synchronization, or unpredictable behavior may
	* occur. For example, in a future release, synchronization may fail.
	*
	* @apiNote
	* {@code 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
	* {@code OptionalDouble} should never itself be {@code null}; it should always point
	* to an {@code OptionalDouble} instance.
	*
	* @since 1.8
	*/
	@jdk.internal.ValueBased
	public final class OptionalDouble {
	/**
	* Common instance for {@code empty()}.
	*/
	private static final OptionalDouble EMPTY = new OptionalDouble();

	/**
	* If true then the value is present, otherwise indicates no value is present
	*/
	private final boolean isPresent;
	private final double value;

	/**
	* Construct an empty instance.
	*
	* @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
	* should exist per VM.
	*/
	private OptionalDouble() {
	this.isPresent = false;
	this.value = Double.NaN;
	}

	/**
	* Returns an empty {@code OptionalDouble} instance. No value is present
	* for this {@code OptionalDouble}.
	*
	* @apiNote
	* Though it may be tempting to do so, avoid testing if an object is empty
	* by comparing with {@code ==} or {@code !=} against instances returned by
	* {@code OptionalDouble.empty()}. There is no guarantee that it is a singleton.
	* Instead, use {@link #isEmpty()} or {@link #isPresent()}.
	*
	* @return an empty {@code OptionalDouble}.
	*/
	public static OptionalDouble empty() {
	return EMPTY;
	}

	/**
	* Construct an instance with the described value.
	*
	* @param value the double value to describe.
	*/
	private OptionalDouble(double value) {
	this.isPresent = true;
	this.value = value;
	}

	/**
	* Returns an {@code OptionalDouble} describing the given value.
	*
	* @param value the value to describe
	* @return an {@code OptionalDouble} with the value present
	*/
	public static OptionalDouble of(double value) {
	return new OptionalDouble(value);
	}

	/**
	* If a value is present, returns the value, otherwise throws
	* {@code NoSuchElementException}.
	*
	* @apiNote
	* The preferred alternative to this method is {@link #orElseThrow()}.
	*
	* @return the value described by this {@code OptionalDouble}
	* @throws NoSuchElementException if no value is present
	*/
	public double getAsDouble() {
	if (!isPresent) {
	throw new NoSuchElementException("No value present");
	}
	return value;
	}

	/**
	* If a value is present, returns {@code true}, otherwise {@code false}.
	*
	* @return {@code true} if a value is present, otherwise {@code false}
	*/
	public boolean isPresent() {
	return isPresent;
	}

	/**
	* If a value is not present, returns {@code true}, otherwise
	* {@code false}.
	*
	* @return {@code true} if a value is not present, otherwise {@code false}
	* @since 11
	*/
	public boolean isEmpty() {
	return !isPresent;
	}

	/**
	* If a value is present, performs the given action with the value,
	* otherwise does nothing.
	*
	* @param action the action to be performed, if a value is present
	* @throws NullPointerException if value is present and the given action is
	* {@code null}
	*/
	public void ifPresent(DoubleConsumer action) {
	if (isPresent) {
	action.accept(value);
	}
	}

	/**
	* If a value is present, performs the given action with the value,
	* otherwise performs the given empty-based action.
	*
	* @param action the action to be performed, if a value is present
	* @param 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 {@code null}, or no value is present and the given empty-based
	* action is {@code null}.
	* @since 9
	*/
	public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
	if (isPresent) {
	action.accept(value);
	} else {
	emptyAction.run();
	}
	}

	/**
	* If a value is present, returns a sequential {@link DoubleStream}
	* containing only that value, otherwise returns an empty
	* {@code DoubleStream}.
	*
	* @apiNote
	* This method can be used to transform a {@code Stream} of optional doubles
	* to a {@code DoubleStream} of present doubles:
	* <pre>{@code
	* Stream<OptionalDouble> os = ..
	* DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
	* }</pre>
	*
	* @return the optional value as a {@code DoubleStream}
	* @since 9
	*/
	public DoubleStream stream() {
	if (isPresent) {
	return DoubleStream.of(value);
	} else {
	return DoubleStream.empty();
	}
	}

	/**
	* If a value is present, returns the value, otherwise returns
	* {@code other}.
	*
	* @param other the value to be returned, if no value is present
	* @return the value, if present, otherwise {@code other}
	*/
	public double orElse(double other) {
	return isPresent ? value : other;
	}

	/**
	* If a value is present, returns the value, otherwise returns the result
	* produced by the supplying function.
	*
	* @param supplier the supplying function that produces a value to be returned
	* @return the value, if present, otherwise the result produced by the
	* supplying function
	* @throws NullPointerException if no value is present and the supplying
	* function is {@code null}
	*/
	public double orElseGet(DoubleSupplier supplier) {
	return isPresent ? value : supplier.getAsDouble();
	}

	/**
	* If a value is present, returns the value, otherwise throws
	* {@code NoSuchElementException}.
	*
	* @return the value described by this {@code OptionalDouble}
	* @throws NoSuchElementException if no value is present
	* @since 10
	*/
	public double orElseThrow() {
	if (!isPresent) {
	throw new NoSuchElementException("No value present");
	}
	return value;
	}

	/**
	* If a value is present, returns the value, otherwise throws an exception
	* produced by the exception supplying function.
	*
	* @apiNote
	* A method reference to the exception constructor with an empty argument
	* list can be used as the supplier. For example,
	* {@code IllegalStateException::new}
	*
	* @param <X> Type of the exception to be thrown
	* @param exceptionSupplier the supplying function that produces an
	* exception to be thrown
	* @return the value, if present
	* @throws X if no value is present
	* @throws NullPointerException if no value is present and the exception
	* supplying function is {@code null}
	*/
	public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
	if (isPresent) {
	return value;
	} else {
	throw exceptionSupplier.get();
	}
	}

	/**
	* Indicates whether some other object is "equal to" this
	* {@code OptionalDouble}. The other object is considered equal if:
	* <ul>
	* <li>it is also an {@code OptionalDouble} and;
	* <li>both instances have no value present or;
	* <li>the present values are "equal to" each other via
	* {@code Double.compare() == 0}.
	* </ul>
	*
	* @param obj an object to be tested for equality
	* @return {@code true} if the other object is "equal to" this object
	* otherwise {@code false}
	*/
	@Override
	public boolean equals(Object obj) {
	if (this == obj) {
	return true;
	}

	return obj instanceof OptionalDouble other
	&& (isPresent && other.isPresent
	? Double.compare(value, other.value) == 0
	: isPresent == other.isPresent);
	}

	/**
	* Returns the hash code of the value, if present, otherwise {@code 0}
	* (zero) if no value is present.
	*
	* @return hash code value of the present value or {@code 0} if no value is
	* present
	*/
	@Override
	public int hashCode() {
	return isPresent ? Double.hashCode(value) : 0;
	}

	/**
	* Returns a non-empty string representation of this {@code OptionalDouble}
	* suitable for debugging. The exact presentation format is unspecified and
	* may vary between implementations and versions.
	*
	* @implSpec
	* If a value is present the result must include its string representation
	* in the result. Empty and present {@code OptionalDouble}s must be
	* unambiguously differentiable.
	*
	* @return the string representation of this instance
	*/
	@Override
	public String toString() {
	return isPresent
	? String.format("OptionalDouble[%s]", value)
	: "OptionalDouble.empty";
	}
	}

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