OSCL-LXR spark-3.0.0/​core/​src/​main/​java/​org/​apache/​spark/​api/​java/​Optional.java	Source navigation Diff markup Identifier search General search
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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.
  */
 
 package org.apache.spark.api.java;
 
 import java.io.Serializable;
 import java.util.Objects;
 
 import com.google.common.base.Preconditions;
 
 /**
  * <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 was not used because at the time, the
  * project did 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 {
 
   private static final Optional<?> EMPTY = new Optional<>();
 
   private final T value;
 
   private Optional() {
     this.value = null;
   }
 
   private Optional(T value) {
     Preconditions.checkNotNull(value);
     this.value = value;
   }
 
   // java.util.Optional API (subset)
 
   /**
    * @return an empty {@code Optional}
    */
   public static <T> Optional<T> empty() {
     @SuppressWarnings("unchecked")
     Optional<T> t = (Optional<T>) EMPTY;
     return t;
   }
 
   /**
    * @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);
   }
 
   /**
    * @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);
     }
   }
 
   /**
    * @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;
   }
 
   /**
    * @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;
   }
 
   /**
    * @return true iff this {@code Optional} contains a value (non-empty)
    */
   public boolean isPresent() {
     return value != null;
   }
 
   // Guava API (subset)
   // of(), get() and isPresent() are identically present in the Guava API
 
   /**
    * @return an empty {@code Optional}
    */
   public static <T> Optional<T> absent() {
     return empty();
   }
 
   /**
    * @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);
   }
 
   /**
    * @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;
   }
 
   /**
    * @return this {@code Optional}'s value if present, or else null
    */
   public T orNull() {
     return value;
   }
 
   // Common methods
 
   @Override
   public boolean equals(Object obj) {
     if (!(obj instanceof Optional)) {
       return false;
     }
     Optional<?> other = (Optional<?>) obj;
     return Objects.equals(value, other.value);
   }
 
   @Override
   public int hashCode() {
     return value == null ? 0 : value.hashCode();
   }
 
   @Override
   public String toString() {
     return value == null ? "Optional.empty" : String.format("Optional[%s]", value);
   }
 
 }

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