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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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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";
 }
}