| /* |
| * 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.Consumer; |
| import java.util.function.Function; |
| import java.util.function.Predicate; |
| import java.util.function.Supplier; |
| |
| // Android-changed: removed ValueBased paragraph. |
| /** |
| * A container object which may or may not contain a non-null value. |
| * If a value is present, {@code isPresent()} will return {@code true} and |
| * {@code get()} will return the value. |
| * |
| * <p>Additional methods that depend on the presence or absence of a contained |
| * value are provided, such as {@link #orElse(java.lang.Object) orElse()} |
| * (return a default value if value not present) and |
| * {@link #ifPresent(java.util.function.Consumer) ifPresent()} (execute a block |
| * of code if the value is present). |
| * |
| * @since 1.8 |
| */ |
| public final class Optional<T> { |
| /** |
| * Common instance for {@code empty()}. |
| */ |
| private static final Optional<?> EMPTY = new Optional<>(); |
| |
| /** |
| * If non-null, the value; if null, indicates no value is present |
| */ |
| private final T value; |
| |
| /** |
| * Constructs an empty instance. |
| * |
| * @implNote Generally only one empty instance, {@link Optional#EMPTY}, |
| * should exist per VM. |
| */ |
| private Optional() { |
| this.value = null; |
| } |
| |
| /** |
| * Returns an empty {@code Optional} instance. No value is present for this |
| * Optional. |
| * |
| * @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()}. |
| * |
| * @param <T> Type of the non-existent value |
| * @return an empty {@code Optional} |
| */ |
| public static<T> Optional<T> empty() { |
| @SuppressWarnings("unchecked") |
| Optional<T> t = (Optional<T>) EMPTY; |
| return t; |
| } |
| |
| /** |
| * Constructs an instance with the value present. |
| * |
| * @param value the non-null value to be present |
| * @throws NullPointerException if value is null |
| */ |
| private Optional(T value) { |
| this.value = Objects.requireNonNull(value); |
| } |
| |
| /** |
| * Returns an {@code Optional} with the specified present non-null value. |
| * |
| * @param <T> the class of the value |
| * @param value the value to be present, which must be non-null |
| * @return an {@code Optional} with the value present |
| * @throws NullPointerException if value is null |
| */ |
| public static <T> Optional<T> of(T value) { |
| return new Optional<>(value); |
| } |
| |
| /** |
| * Returns an {@code Optional} describing the specified value, if non-null, |
| * otherwise returns an empty {@code Optional}. |
| * |
| * @param <T> the class of the value |
| * @param value the possibly-null value to describe |
| * @return an {@code Optional} with a present value if the specified value |
| * is non-null, otherwise an empty {@code Optional} |
| */ |
| public static <T> Optional<T> ofNullable(T value) { |
| return value == null ? empty() : of(value); |
| } |
| |
| /** |
| * If a value is present in this {@code Optional}, returns the value, |
| * otherwise throws {@code NoSuchElementException}. |
| * |
| * @return the non-null value held by this {@code Optional} |
| * @throws NoSuchElementException if there is no value present |
| * |
| * @see Optional#isPresent() |
| */ |
| public T get() { |
| if (value == null) { |
| 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 value != null; |
| } |
| |
| /** |
| * If a value is present, invoke the specified consumer with the value, |
| * 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(Consumer<? super T> consumer) { |
| if (value != null) |
| consumer.accept(value); |
| } |
| |
| /** |
| * If a value is present, and the value matches the given predicate, |
| * return an {@code Optional} describing the value, otherwise return an |
| * empty {@code Optional}. |
| * |
| * @param predicate a predicate to apply to the value, if present |
| * @return an {@code Optional} describing the value of this {@code Optional} |
| * if a value is present and the value matches the given predicate, |
| * otherwise an empty {@code Optional} |
| * @throws NullPointerException if the predicate is null |
| */ |
| public Optional<T> filter(Predicate<? super T> predicate) { |
| Objects.requireNonNull(predicate); |
| if (!isPresent()) |
| return this; |
| else |
| return predicate.test(value) ? this : empty(); |
| } |
| |
| /** |
| * If a value is present, apply the provided mapping function to it, |
| * and if the result is non-null, return an {@code Optional} describing the |
| * result. Otherwise return an empty {@code Optional}. |
| * |
| * @apiNote This method supports post-processing on optional values, without |
| * the need to explicitly check for a return status. For example, the |
| * following code traverses a stream of file names, selects one that has |
| * not yet been processed, and then opens that file, returning an |
| * {@code Optional<FileInputStream>}: |
| * |
| * <pre>{@code |
| * Optional<FileInputStream> fis = |
| * names.stream().filter(name -> !isProcessedYet(name)) |
| * .findFirst() |
| * .map(name -> new FileInputStream(name)); |
| * }</pre> |
| * |
| * Here, {@code findFirst} returns an {@code Optional<String>}, and then |
| * {@code map} returns an {@code Optional<FileInputStream>} for the desired |
| * file if one exists. |
| * |
| * @param <U> The type of the result of the mapping function |
| * @param mapper a mapping function to apply to the value, if present |
| * @return an {@code Optional} describing the result of applying a mapping |
| * function to the value of this {@code Optional}, if a value is present, |
| * otherwise an empty {@code Optional} |
| * @throws NullPointerException if the mapping function is null |
| */ |
| public<U> Optional<U> map(Function<? super T, ? extends U> mapper) { |
| Objects.requireNonNull(mapper); |
| if (!isPresent()) |
| return empty(); |
| else { |
| return Optional.ofNullable(mapper.apply(value)); |
| } |
| } |
| |
| /** |
| * If a value is present, apply the provided {@code Optional}-bearing |
| * mapping function to it, return that result, otherwise return an empty |
| * {@code Optional}. This method is similar to {@link #map(Function)}, |
| * but the provided mapper is one whose result is already an {@code Optional}, |
| * and if invoked, {@code flatMap} does not wrap it with an additional |
| * {@code Optional}. |
| * |
| * @param <U> The type parameter to the {@code Optional} returned by |
| * @param mapper a mapping function to apply to the value, if present |
| * the mapping function |
| * @return the result of applying an {@code Optional}-bearing mapping |
| * function to the value of this {@code Optional}, if a value is present, |
| * otherwise an empty {@code Optional} |
| * @throws NullPointerException if the mapping function is null or returns |
| * a null result |
| */ |
| public<U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper) { |
| Objects.requireNonNull(mapper); |
| if (!isPresent()) |
| return empty(); |
| else { |
| return Objects.requireNonNull(mapper.apply(value)); |
| } |
| } |
| |
| /** |
| * Return the value if present, otherwise return {@code other}. |
| * |
| * @param other the value to be returned if there is no value present, may |
| * be null |
| * @return the value, if present, otherwise {@code other} |
| */ |
| public T orElse(T other) { |
| return value != null ? value : other; |
| } |
| |
| /** |
| * Return the value if present, otherwise invoke {@code other} and return |
| * the result of that invocation. |
| * |
| * @param other a {@code Supplier} whose result is returned if no value |
| * is present |
| * @return the value if present otherwise the result of {@code other.get()} |
| * @throws NullPointerException if value is not present and {@code other} is |
| * null |
| */ |
| public T orElseGet(Supplier<? extends T> other) { |
| return value != null ? value : other.get(); |
| } |
| |
| /** |
| * 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> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { |
| if (value != null) { |
| return value; |
| } else { |
| throw exceptionSupplier.get(); |
| } |
| } |
| |
| /** |
| * Indicates whether some other object is "equal to" this Optional. The |
| * other object is considered equal if: |
| * <ul> |
| * <li>it is also an {@code Optional} and; |
| * <li>both instances have no value present or; |
| * <li>the present values are "equal to" each other via {@code equals()}. |
| * </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 Optional)) { |
| return false; |
| } |
| |
| Optional<?> other = (Optional<?>) obj; |
| return Objects.equals(value, other.value); |
| } |
| |
| /** |
| * 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 Objects.hashCode(value); |
| } |
| |
| /** |
| * Returns a non-empty string representation of this Optional 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 Optionals must be |
| * unambiguously differentiable. |
| * |
| * @return the string representation of this instance |
| */ |
| @Override |
| public String toString() { |
| return value != null |
| ? String.format("Optional[%s]", value) |
| : "Optional.empty"; |
| } |
| } |