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 * 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,

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 *

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 */

package java.util;

import java.util.function.LongConsumer;

import java.util.function.LongSupplier;

import java.util.function.Supplier;

import java.util.stream.LongStream;

/**

 * A container object which may or may not contain a {@code long} value.

 * If a value is present, {@code isPresent()} will return {@code true} and

 * {@code getAsLong()} will return the value.

 *

 * <p>Additional methods that depend on the presence or absence of a contained

 * value are provided, such as {@link #orElse(long) orElse()}

 * (return a default value if value not present) and

 * {@link #ifPresent(java.util.function.LongConsumer) ifPresent()} (perform an

 * action 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 OptionalLong} may have unpredictable results and should be avoided.

 *

 * @since 1.8

 */

public final class OptionalLong {

    /**

     * Common instance for {@code empty()}.

     */

    private static final OptionalLong EMPTY = new OptionalLong();

    /**

     * If true then the value is present, otherwise indicates no value is present

     */

    private final boolean isPresent;

    private final long value;

    /**

     * Construct an empty instance.

     *

     * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},

     * should exist per VM.

     */

    private OptionalLong() {

        this.isPresent = false;

        this.value = 0;

    }

    /**

     * Returns an empty {@code OptionalLong} instance.  No value is present for this

     * OptionalLong.

     *

     * @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 OptionalLong}.

     */

    public static OptionalLong empty() {

        return EMPTY;

    }

    /**

     * Construct an instance with the value present.

     *

     * @param value the long value to be present

     */

    private OptionalLong(long value) {

        this.isPresent = true;

        this.value = value;

    }

    /**

     * Return an {@code OptionalLong} with the specified value present.

     *

     * @param value the value to be present

     * @return an {@code OptionalLong} with the value present

     */

    public static OptionalLong of(long value) {

        return new OptionalLong(value);

    }

    /**

     * If a value is present in this {@code OptionalLong}, returns the value,

     * otherwise throws {@code NoSuchElementException}.

     *

     * @return the value held by this {@code OptionalLong}

     * @throws NoSuchElementException if there is no value present

     *

     * @see OptionalLong#isPresent()

     */

    public long getAsLong() {

        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;

    }

    /**

     * If a value is present, perform the given action with the value,

     * otherwise do nothing.

     *

     * @param action the action to be performed if a value is present

     * @throws NullPointerException if a value is present and {@code action} is

     * null

     */

    public void ifPresent(LongConsumer action) {

        if (isPresent) {

            action.accept(value);

        }

    }

    /**

     * If a value is present, perform the given action with the value,

     * otherwise perform 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 a value is

     * not present

     * @throws NullPointerException if a value is present and {@code action} is

     * null, or a value is not present and {@code emptyAction} is null.

     * @since 1.9

     */

    public void ifPresentOrElse(LongConsumer action, Runnable emptyAction) {

        if (isPresent) {

            action.accept(value);

        } else {

            emptyAction.run();

        }

    }

    /**

     * If a value is present return a sequential {@link LongStream} containing

     * only that value, otherwise return an empty {@code LongStream}.

     *

     * @apiNote This method can be used to transform a {@code Stream} of

     * optional longs to a {@code LongStream} of present longs:

     *

     * <pre>{@code

     *     Stream<OptionalLong> os = ..

     *     LongStream s = os.flatMapToLong(OptionalLong::stream)

     * }</pre>

     *

     * @return the optional value as a {@code LongStream}

     * @since 1.9

     */

    public LongStream stream() {

        if (isPresent) {

            return LongStream.of(value);

        } else {

            return LongStream.empty();

        }

    }

    /**

     * 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 long orElse(long 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 LongSupplier} whose result is returned if no value

     * is present

     * @return the value if present otherwise the result of {@code other.getAsLong()}

     * @throws NullPointerException if value is not present and {@code other} is

     * null

     */

    public long orElseGet(LongSupplier other) {

        return isPresent ? value : other.getAsLong();

    }

    /**

     * 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> long orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {

        if (isPresent) {

            return value;

        } else {

            throw exceptionSupplier.get();

        }

    }

    /**

     * Indicates whether some other object is "equal to" this OptionalLong. The

     * other object is considered equal if:

     * <ul>

     * <li>it is also an {@code OptionalLong} and;

     * <li>both instances have no value present or;

     * <li>the present values are "equal to" each other via {@code ==}.

     * </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 OptionalLong)) {

            return false;

        }

        OptionalLong other = (OptionalLong) obj;

        return (isPresent && other.isPresent)

                ? value == other.value

                : 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 ? Long.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("OptionalLong[%s]", value)

                : "OptionalLong.empty";

    }

}