| /* |
| * 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.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()} 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(long) orElse()} |
| * (returns a default value if no value is present) and |
| * {@link #ifPresent(LongConsumer) ifPresent()} (performs an |
| * action if a value is present). |
| * |
| * <p>This is a <a href="https://docs.oracle.com/en/java/javase/17/docs/api/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 OptionalLong} 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 OptionalLong} should never itself be {@code null}; it should always point |
| * to an {@code OptionalLong} instance. |
| * |
| * @since 1.8 |
| */ |
| @jdk.internal.ValueBased |
| 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 {@code OptionalLong}. |
| * |
| * @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 OptionalLong.empty()}. There is no guarantee that it is a singleton. |
| * Instead, use {@link #isEmpty()} or {@link #isPresent()}. |
| * |
| * @return an empty {@code OptionalLong}. |
| */ |
| public static OptionalLong empty() { |
| return EMPTY; |
| } |
| |
| /** |
| * Construct an instance with the described value. |
| * |
| * @param value the long value to describe |
| */ |
| private OptionalLong(long value) { |
| this.isPresent = true; |
| this.value = value; |
| } |
| |
| /** |
| * Returns an {@code OptionalLong} describing the given value. |
| * |
| * @param value the value to describe |
| * @return an {@code OptionalLong} with the value present |
| */ |
| public static OptionalLong of(long value) { |
| return new OptionalLong(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 OptionalLong} |
| * @throws NoSuchElementException if no value is present |
| */ |
| public long getAsLong() { |
| 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(LongConsumer 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(LongConsumer action, Runnable emptyAction) { |
| if (isPresent) { |
| action.accept(value); |
| } else { |
| emptyAction.run(); |
| } |
| } |
| |
| /** |
| * If a value is present, returns a sequential {@link LongStream} containing |
| * only that value, otherwise returns an empty {@code LongStream}. |
| * |
| * @apiNote |
| * This method can be used to transform a {@code Stream} of optional longs |
| * to an {@code LongStream} of present longs: |
| * <pre>{@code |
| * Stream<OptionalLong> os = .. |
| * LongStream s = os.flatMapToLong(OptionalLong::stream) |
| * }</pre> |
| * |
| * @return the optional value as an {@code LongStream} |
| * @since 9 |
| */ |
| public LongStream stream() { |
| if (isPresent) { |
| return LongStream.of(value); |
| } else { |
| return LongStream.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 long orElse(long 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 long orElseGet(LongSupplier supplier) { |
| return isPresent ? value : supplier.getAsLong(); |
| } |
| |
| /** |
| * If a value is present, returns the value, otherwise throws |
| * {@code NoSuchElementException}. |
| * |
| * @return the value described by this {@code OptionalLong} |
| * @throws NoSuchElementException if no value is present |
| * @since 10 |
| */ |
| public long 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> 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 |
| * {@code 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; |
| } |
| |
| return obj instanceof OptionalLong other |
| && (isPresent && other.isPresent |
| ? value == other.value |
| : 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 ? Long.hashCode(value) : 0; |
| } |
| |
| /** |
| * Returns a non-empty string representation of this {@code OptionalLong} |
| * 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 OptionalLong}s must be |
| * unambiguously differentiable. |
| * |
| * @return the string representation of this instance |
| */ |
| @Override |
| public String toString() { |
| return isPresent |
| ? ("OptionalLong[" + value + "]") |
| : "OptionalLong.empty"; |
| } |
| } |
