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	/*
	* Copyright (c) 2012, 2013, 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;

	/**
	* A container object which may or may not contain a {@code double} value.
	* If a value is present, {@code isPresent()} will return {@code true} and
	* {@code getAsDouble()} will return the value.
	*
	* <p>Additional methods that depend on the presence or absence of a contained
	* value are provided, such as {@link #orElse(double) orElse()}
	* (return a default value if value not present) and
	* {@link #ifPresent(java.util.function.DoubleConsumer) ifPresent()} (execute a block
	* of code if the value is present).
	*
	* <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
	* class; use of identity-sensitive operations (including reference equality
	* ({@code ==}), identity hash code, or synchronization) on instances of
	* {@code OptionalDouble} may have unpredictable results and should be avoided.
	*
	* @since 1.8
	*/
	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
	* OptionalDouble.
	*
	* @apiNote Though it may be tempting to do so, avoid testing if an object
	* is empty by comparing with {@code ==} against instances returned by
	* {@code Option.empty()}. There is no guarantee that it is a singleton.
	* Instead, use {@link #isPresent()}.
	*
	* @return an empty {@code OptionalDouble}.
	*/
	public static OptionalDouble empty() {
	return EMPTY;
	}

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

	/**
	* Return an {@code OptionalDouble} with the specified value present.
	*
	* @param value the value to be present
	* @return an {@code OptionalDouble} with the value present
	*/
	public static OptionalDouble of(double value) {
	return new OptionalDouble(value);
	}

	/**
	* If a value is present in this {@code OptionalDouble}, returns the value,
	* otherwise throws {@code NoSuchElementException}.
	*
	* @return the value held by this {@code OptionalDouble}
	* @throws NoSuchElementException if there is no value present
	*
	* @see OptionalDouble#isPresent()
	*/
	public double getAsDouble() {
	if (!isPresent) {
	throw new NoSuchElementException("No value present");
	}
	return value;
	}

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

	/**
	* Have the specified consumer accept the value if a value is present,
	* otherwise do nothing.
	*
	* @param consumer block to be executed if a value is present
	* @throws NullPointerException if value is present and {@code consumer} is
	* null
	*/
	public void ifPresent(DoubleConsumer consumer) {
	if (isPresent)
	consumer.accept(value);
	}

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

	/**
	* Return the value if present, otherwise invoke {@code other} and return
	* the result of that invocation.
	*
	* @param other a {@code DoubleSupplier} whose result is returned if no value
	* is present
	* @return the value if present otherwise the result of {@code other.getAsDouble()}
	* @throws NullPointerException if value is not present and {@code other} is
	* null
	*/
	public double orElseGet(DoubleSupplier other) {
	return isPresent ? value : other.getAsDouble();
	}

	/**
	* Return the contained value, if present, otherwise throw an exception
	* to be created by the provided supplier.
	*
	* @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 supplier which will return the exception to
	* be thrown
	* @return the present value
	* @throws X if there is no value present
	* @throws NullPointerException if no value is present and
	* {@code exceptionSupplier} is null
	*/
	public<X extends Throwable> double orElseThrow(Supplier<X> exceptionSupplier) throws X {
	if (isPresent) {
	return value;
	} else {
	throw exceptionSupplier.get();
	}
	}

	/**
	* Indicates whether some other object is "equal to" this 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;
	}

	if (!(obj instanceof OptionalDouble)) {
	return false;
	}

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

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

	/**
	* {@inheritDoc}
	*
	* 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.
	*
	* @implSpec If a value is present the result must include its string
	* representation in the result. Empty and present instances 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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