| /* |
| * Copyright 2015 Google Inc. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); you may not |
| * use this file except in compliance with the License. You may obtain a copy of |
| * the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT |
| * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| * License for the specific language governing permissions and limitations under |
| * the License. |
| */ |
| package java.util; |
| |
| import java.util.function.Consumer; |
| import java.util.function.Function; |
| import java.util.function.Predicate; |
| import java.util.function.Supplier; |
| |
| import static javaemul.internal.InternalPreconditions.checkCriticalElement; |
| import static javaemul.internal.InternalPreconditions.checkCriticalNotNull; |
| import static javaemul.internal.InternalPreconditions.checkNotNull; |
| |
| /** |
| * See <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html"> |
| * the official Java API doc</a> for details. |
| * |
| * @param <T> type of the wrapped reference |
| */ |
| public final class Optional<T> { |
| |
| @SuppressWarnings("unchecked") |
| public static <T> Optional<T> empty() { |
| return (Optional<T>) EMPTY; |
| } |
| |
| public static <T> Optional<T> of(T value) { |
| return new Optional<>(checkCriticalNotNull(value)); |
| } |
| |
| public static <T> Optional<T> ofNullable(T value) { |
| return value == null ? empty() : of(value); |
| } |
| |
| private static final Optional<?> EMPTY = new Optional<>(null); |
| |
| private final T ref; |
| |
| private Optional(T ref) { |
| this.ref = ref; |
| } |
| |
| public boolean isPresent() { |
| return ref != null; |
| } |
| |
| public T get() { |
| checkCriticalElement(isPresent()); |
| return ref; |
| } |
| |
| public void ifPresent(Consumer<? super T> consumer) { |
| if (isPresent()) { |
| consumer.accept(ref); |
| } |
| } |
| |
| public Optional<T> filter(Predicate<? super T> predicate) { |
| checkNotNull(predicate); |
| if (!isPresent() || predicate.test(ref)) { |
| return this; |
| } |
| return empty(); |
| } |
| |
| public <U> Optional<U> map(Function<? super T, ? extends U> mapper) { |
| checkNotNull(mapper); |
| if (isPresent()) { |
| return ofNullable(mapper.apply(ref)); |
| } |
| return empty(); |
| } |
| |
| public <U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper) { |
| checkNotNull(mapper); |
| if (isPresent()) { |
| return checkNotNull(mapper.apply(ref)); |
| } |
| return empty(); |
| } |
| |
| public T orElse(T other) { |
| return isPresent() ? ref : other; |
| } |
| |
| public T orElseGet(Supplier<? extends T> other) { |
| return isPresent() ? ref : other.get(); |
| } |
| |
| public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { |
| if (isPresent()) { |
| return ref; |
| } |
| throw exceptionSupplier.get(); |
| } |
| |
| @Override |
| public boolean equals(Object obj) { |
| if (obj == this) { |
| return true; |
| } |
| if (!(obj instanceof Optional)) { |
| return false; |
| } |
| Optional<?> other = (Optional<?>) obj; |
| return Objects.equals(ref, other.ref); |
| } |
| |
| @Override |
| public int hashCode() { |
| return Objects.hashCode(ref); |
| } |
| |
| @Override |
| public String toString() { |
| return isPresent() ? "Optional.of(" + String.valueOf(ref) + ")" : "Optional.empty()"; |
| } |
| } |