Source code

001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.util;
020
021import net.jcip.annotations.Immutable;
022import net.jcip.annotations.ThreadSafe;
023
024import java.io.Serializable;
025
026/**
027 * Represents an optional value. Loosely based on
028 * <a href="http://download.java.net/jdk8/docs/api/java/util/Optional.html"></a>The Java 8 version</a>, but filtered for
029 * Java 7 compatibility.
030 */
031@Immutable
032@ThreadSafe
033public final class Optional<T> implements Serializable {
034
035  private static final long serialVersionUID = 42L;
036
037  private final T value;
038  private final String valueStr;
039  private final int valueHash;
040
041  private Optional(final T value) {
042    this.value = value;
043    this.valueStr = "Optional:{" + value + '}';
044    this.valueHash = value.hashCode();
045  }
046
047  private Optional() {
048    this.value = null;
049    this.valueStr = "OptionalvNothing";
050    this.valueHash = 0;
051  }
052
053  /**
054   * @return An Optional with the given value.
055   * @throws NullPointerException if the value is null
056   */
057  public static <T> Optional<T> of(final T value) throws NullPointerException {
058    if (null == value) {
059      throw new NullPointerException("Passed a null value. Use ofNullable() instead");
060    }
061    return new Optional<>(value);
062  }
063
064  /**
065   * @return an Optional with no value.
066   */
067  public static <T> Optional<T> empty() {
068    return new Optional<>();
069  }
070
071  /**
072   * @return An optional representing the given value, or an empty Optional.
073   */
074  public static <T> Optional<T> ofNullable(final T value) {
075    if (null == value) {
076      return Optional.empty();
077    } else {
078      return Optional.of(value);
079    }
080  }
081
082  /**
083   * @return the value represented or null, if isPresent() is false.
084   */
085  public T get() {
086    return this.value;
087  }
088
089  /**
090   * @param other
091   * @return the value of this Optional or other, if no value exists.
092   */
093  public T orElse(final T other) {
094    if (isPresent()) {
095      return this.get();
096    } else {
097      return other;
098    }
099  }
100
101  /**
102   * @return true if there is a value, false otherwise.
103   */
104  public boolean isPresent() {
105    return null != this.value;
106  }
107
108  @Override
109  public boolean equals(final Object obj) {
110
111    if (this == obj) return true;
112
113    if (obj == null || getClass() != obj.getClass()) return false;
114
115    final Optional that = (Optional) obj;
116    return this.value == that.value || (this.value != null && this.value.equals(that.value));
117  }
118
119  @Override
120  public int hashCode() {
121    return this.valueHash;
122  }
123
124  @Override
125  public String toString() {
126    return this.valueStr;
127  }
128}