001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.base;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018
019import com.google.common.annotations.GwtCompatible;
020import com.google.common.annotations.GwtIncompatible;
021import java.io.Serializable;
022import java.lang.ref.WeakReference;
023import java.lang.reflect.Field;
024import java.util.EnumSet;
025import java.util.HashMap;
026import java.util.Map;
027import java.util.WeakHashMap;
028import org.checkerframework.checker.nullness.qual.Nullable;
029
030/**
031 * Utility methods for working with {@link Enum} instances.
032 *
033 * @author Steve McKay
034 * @since 9.0
035 */
036@GwtCompatible(emulated = true)
037public final class Enums {
038
039  private Enums() {}
040
041  /**
042   * Returns the {@link Field} in which {@code enumValue} is defined. For example, to get the {@code
043   * Description} annotation on the {@code GOLF} constant of enum {@code Sport}, use {@code
044   * Enums.getField(Sport.GOLF).getAnnotation(Description.class)}.
045   *
046   * @since 12.0
047   */
048  @GwtIncompatible // reflection
049  public static Field getField(Enum<?> enumValue) {
050    Class<?> clazz = enumValue.getDeclaringClass();
051    try {
052      return clazz.getDeclaredField(enumValue.name());
053    } catch (NoSuchFieldException impossible) {
054      throw new AssertionError(impossible);
055    }
056  }
057
058  /**
059   * Returns an optional enum constant for the given type, using {@link Enum#valueOf}. If the
060   * constant does not exist, {@link Optional#absent} is returned. A common use case is for parsing
061   * user input or falling back to a default enum constant. For example, {@code
062   * Enums.getIfPresent(Country.class, countryInput).or(Country.DEFAULT);}
063   *
064   * @since 12.0
065   */
066  public static <T extends Enum<T>> Optional<T> getIfPresent(Class<T> enumClass, String value) {
067    checkNotNull(enumClass);
068    checkNotNull(value);
069    return Platform.getEnumIfPresent(enumClass, value);
070  }
071
072  @GwtIncompatible // java.lang.ref.WeakReference
073  private static final Map<Class<? extends Enum<?>>, Map<String, WeakReference<? extends Enum<?>>>>
074      enumConstantCache = new WeakHashMap<>();
075
076  @GwtIncompatible // java.lang.ref.WeakReference
077  private static <T extends Enum<T>> Map<String, WeakReference<? extends Enum<?>>> populateCache(
078      Class<T> enumClass) {
079    Map<String, WeakReference<? extends Enum<?>>> result = new HashMap<>();
080    for (T enumInstance : EnumSet.allOf(enumClass)) {
081      result.put(enumInstance.name(), new WeakReference<Enum<?>>(enumInstance));
082    }
083    enumConstantCache.put(enumClass, result);
084    return result;
085  }
086
087  @GwtIncompatible // java.lang.ref.WeakReference
088  static <T extends Enum<T>> Map<String, WeakReference<? extends Enum<?>>> getEnumConstants(
089      Class<T> enumClass) {
090    synchronized (enumConstantCache) {
091      Map<String, WeakReference<? extends Enum<?>>> constants = enumConstantCache.get(enumClass);
092      if (constants == null) {
093        constants = populateCache(enumClass);
094      }
095      return constants;
096    }
097  }
098
099  /**
100   * Returns a converter that converts between strings and {@code enum} values of type {@code
101   * enumClass} using {@link Enum#valueOf(Class, String)} and {@link Enum#name()}. The converter
102   * will throw an {@code IllegalArgumentException} if the argument is not the name of any enum
103   * constant in the specified enum.
104   *
105   * @since 16.0
106   */
107  public static <T extends Enum<T>> Converter<String, T> stringConverter(final Class<T> enumClass) {
108    return new StringConverter<T>(enumClass);
109  }
110
111  private static final class StringConverter<T extends Enum<T>> extends Converter<String, T>
112      implements Serializable {
113
114    private final Class<T> enumClass;
115
116    StringConverter(Class<T> enumClass) {
117      this.enumClass = checkNotNull(enumClass);
118    }
119
120    @Override
121    protected T doForward(String value) {
122      return Enum.valueOf(enumClass, value);
123    }
124
125    @Override
126    protected String doBackward(T enumValue) {
127      return enumValue.name();
128    }
129
130    @Override
131    public boolean equals(@Nullable Object object) {
132      if (object instanceof StringConverter) {
133        StringConverter<?> that = (StringConverter<?>) object;
134        return this.enumClass.equals(that.enumClass);
135      }
136      return false;
137    }
138
139    @Override
140    public int hashCode() {
141      return enumClass.hashCode();
142    }
143
144    @Override
145    public String toString() {
146      return "Enums.stringConverter(" + enumClass.getName() + ".class)";
147    }
148
149    private static final long serialVersionUID = 0L;
150  }
151}