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.GwtIncompatible;
020import com.google.common.annotations.J2ktIncompatible;
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.jspecify.annotations.Nullable;
029
030/**
031 * Utility methods for working with {@link Enum} instances.
032 *
033 * @author Steve McKay
034 * @since 9.0
035 */
036@GwtIncompatible
037@J2ktIncompatible
038public final class Enums {
039
040  private Enums() {}
041
042  /**
043   * Returns the {@link Field} in which {@code enumValue} is defined. For example, to get the {@code
044   * Description} annotation on the {@code GOLF} constant of enum {@code Sport}, use {@code
045   * Enums.getField(Sport.GOLF).getAnnotation(Description.class)}.
046   *
047   * @since 12.0
048   */
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  private static final Map<Class<? extends Enum<?>>, Map<String, WeakReference<? extends Enum<?>>>>
073      enumConstantCache = new WeakHashMap<>();
074
075  private static <T extends Enum<T>> Map<String, WeakReference<? extends Enum<?>>> populateCache(
076      Class<T> enumClass) {
077    Map<String, WeakReference<? extends Enum<?>>> result = new HashMap<>();
078    for (T enumInstance : EnumSet.allOf(enumClass)) {
079      result.put(enumInstance.name(), new WeakReference<Enum<?>>(enumInstance));
080    }
081    enumConstantCache.put(enumClass, result);
082    return result;
083  }
084
085  static <T extends Enum<T>> Map<String, WeakReference<? extends Enum<?>>> getEnumConstants(
086      Class<T> enumClass) {
087    synchronized (enumConstantCache) {
088      Map<String, WeakReference<? extends Enum<?>>> constants = enumConstantCache.get(enumClass);
089      if (constants == null) {
090        constants = populateCache(enumClass);
091      }
092      return constants;
093    }
094  }
095
096  /**
097   * Returns a serializable converter that converts between strings and {@code enum} values of type
098   * {@code enumClass} using {@link Enum#valueOf(Class, String)} and {@link Enum#name()}. The
099   * converter will throw an {@code IllegalArgumentException} if the argument is not the name of any
100   * enum constant in the specified enum.
101   *
102   * @since 16.0
103   */
104  public static <T extends Enum<T>> Converter<String, T> stringConverter(Class<T> enumClass) {
105    return new StringConverter<>(enumClass);
106  }
107
108  private static final class StringConverter<T extends Enum<T>> extends Converter<String, T>
109      implements Serializable {
110
111    private final Class<T> enumClass;
112
113    StringConverter(Class<T> enumClass) {
114      this.enumClass = checkNotNull(enumClass);
115    }
116
117    @Override
118    protected T doForward(String value) {
119      return Enum.valueOf(enumClass, value);
120    }
121
122    @Override
123    protected String doBackward(T enumValue) {
124      return enumValue.name();
125    }
126
127    @Override
128    public boolean equals(@Nullable Object obj) {
129      if (obj instanceof StringConverter) {
130        StringConverter<?> that = (StringConverter<?>) obj;
131        return this.enumClass.equals(that.enumClass);
132      }
133      return false;
134    }
135
136    @Override
137    public int hashCode() {
138      return enumClass.hashCode();
139    }
140
141    @Override
142    public String toString() {
143      return "Enums.stringConverter(" + enumClass.getName() + ".class)";
144    }
145
146    private static final long serialVersionUID = 0L;
147  }
148}