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187
core/src/main/java/org/apache/spark/api/java/Optional.java
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one or more | ||
| * contributor license agreements. See the NOTICE file distributed with | ||
| * this work for additional information regarding copyright ownership. | ||
| * The ASF licenses this file to You 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. | ||
| */ | ||
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| package org.apache.spark.api.java; | ||
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| import java.io.Serializable; | ||
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| import com.google.common.base.Preconditions; | ||
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| /** | ||
| * <p>Like {@code java.util.Optional} in Java 8, {@code scala.Option} in Scala, and | ||
| * {@code com.google.common.base.Optional} in Google Guava, this class represents a | ||
| * value of a given type that may or may not exist. It is used in methods that wish | ||
| * to optionally return a value, in preference to returning {@code null}.</p> | ||
| * | ||
| * <p>In fact, the class here is a reimplementation of the essential API of both | ||
| * {@code java.util.Optional} and {@code com.google.common.base.Optional}. From | ||
| * {@code java.util.Optional}, it implements:</p> | ||
| * | ||
| * <ul> | ||
| * <li>{@link #empty()}</li> | ||
| * <li>{@link #of(Object)}</li> | ||
| * <li>{@link #ofNullable(Object)}</li> | ||
| * <li>{@link #get()}</li> | ||
| * <li>{@link #orElse(Object)}</li> | ||
| * <li>{@link #isPresent()}</li> | ||
| * </ul> | ||
| * | ||
| * <p>From {@code com.google.common.base.Optional} it implements:</p> | ||
| * | ||
| * <ul> | ||
| * <li>{@link #absent()}</li> | ||
| * <li>{@link #of(Object)}</li> | ||
| * <li>{@link #fromNullable(Object)}</li> | ||
| * <li>{@link #get()}</li> | ||
| * <li>{@link #or(Object)}</li> | ||
| * <li>{@link #orNull()}</li> | ||
| * <li>{@link #isPresent()}</li> | ||
| * </ul> | ||
| * | ||
| * <p>{@code java.util.Optional} itself is not used at this time because the | ||
| * project does not require Java 8. Using {@code com.google.common.base.Optional} | ||
| * has in the past caused serious library version conflicts with Guava that can't | ||
| * be resolved by shading. Hence this work-alike clone.</p> | ||
| * | ||
| * @param <T> type of value held inside | ||
| */ | ||
| public final class Optional<T> implements Serializable { | ||
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| private static final Optional<?> EMPTY = new Optional<>(); | ||
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| private final T value; | ||
|
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| private Optional() { | ||
| this.value = null; | ||
| } | ||
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| private Optional(T value) { | ||
| Preconditions.checkNotNull(value); | ||
| this.value = value; | ||
| } | ||
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| // java.util.Optional API (subset) | ||
|
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| /** | ||
| * @return an empty {@code Optional} | ||
| */ | ||
| public static <T> Optional<T> empty() { | ||
| @SuppressWarnings("unchecked") | ||
| Optional<T> t = (Optional<T>) EMPTY; | ||
| return t; | ||
| } | ||
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| /** | ||
| * @param value non-null value to wrap | ||
| * @return {@code Optional} wrapping this value | ||
| * @throws NullPointerException if value is null | ||
| */ | ||
| public static <T> Optional<T> of(T value) { | ||
| return new Optional<>(value); | ||
| } | ||
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| /** | ||
| * @param value value to wrap, which may be null | ||
| * @return {@code Optional} wrapping this value, which may be empty | ||
| */ | ||
| public static <T> Optional<T> ofNullable(T value) { | ||
| if (value == null) { | ||
| return empty(); | ||
| } else { | ||
| return of(value); | ||
| } | ||
| } | ||
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| /** | ||
| * @return the value wrapped by this {@code Optional} | ||
| * @throws NullPointerException if this is empty (contains no value) | ||
| */ | ||
| public T get() { | ||
| Preconditions.checkNotNull(value); | ||
| return value; | ||
| } | ||
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| /** | ||
| * @param other value to return if this is empty | ||
| * @return this {@code Optional}'s value if present, or else the given value | ||
| */ | ||
| public T orElse(T other) { | ||
| return value != null ? value : other; | ||
| } | ||
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| /** | ||
| * @return true iff this {@code Optional} contains a value (non-empty) | ||
| */ | ||
| public boolean isPresent() { | ||
| return value != null; | ||
| } | ||
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| // Guava API (subset) | ||
| // of(), get() and isPresent() are identically present in the Guava API | ||
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| /** | ||
| * @return an empty {@code Optional} | ||
| */ | ||
| public static <T> Optional<T> absent() { | ||
| return empty(); | ||
| } | ||
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| /** | ||
| * @param value value to wrap, which may be null | ||
| * @return {@code Optional} wrapping this value, which may be empty | ||
| */ | ||
| public static <T> Optional<T> fromNullable(T value) { | ||
| return ofNullable(value); | ||
| } | ||
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| /** | ||
| * @param other value to return if this is empty | ||
| * @return this {@code Optional}'s value if present, or else the given value | ||
| */ | ||
| public T or(T other) { | ||
| return value != null ? value : other; | ||
| } | ||
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| /** | ||
| * @return this {@code Optional}'s value if present, or else null | ||
| */ | ||
| public T orNull() { | ||
| return value; | ||
| } | ||
|
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| // Common methods | ||
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| @Override | ||
| public boolean equals(Object obj) { | ||
| if (!(obj instanceof Optional)) { | ||
| return false; | ||
| } | ||
| Optional<?> other = (Optional<?>) obj; | ||
| return value == null ? other.value == null : value.equals(other.value); | ||
| } | ||
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| @Override | ||
| public int hashCode() { | ||
| return value == null ? 0 : value.hashCode(); | ||
| } | ||
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| @Override | ||
| public String toString() { | ||
| return value == null ? "Optional.empty" : String.format("Optional[%s]", value); | ||
| } | ||
|
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| } |
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