com.google.common.base.Enums.java Source code

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Here is the source code for com.google.common.base.Enums.java

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/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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 com.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

import java.io.Serializable;
import java.lang.ref.WeakReference;
import java.lang.reflect.Field;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;

import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;

/**
 * Utility methods for working with {@link Enum} instances.
 *
 * @author Steve McKay
 *
 * @since 9.0
 */
@CheckReturnValue
@GwtCompatible(emulated = true)
@Beta
public final class Enums {

    private Enums() {
    }

    /**
     * Returns the {@link Field} in which {@code enumValue} is defined. For example, to get the
     * {@code Description} annotation on the {@code GOLF} constant of enum {@code Sport}, use
     * {@code Enums.getField(Sport.GOLF).getAnnotation(Description.class)}.
     *
     * @since 12.0
     */
    @GwtIncompatible("reflection")
    public static Field getField(Enum<?> enumValue) {
        Class<?> clazz = enumValue.getDeclaringClass();
        try {
            return clazz.getDeclaredField(enumValue.name());
        } catch (NoSuchFieldException impossible) {
            throw new AssertionError(impossible);
        }
    }

    /**
     * Returns an optional enum constant for the given type, using {@link Enum#valueOf}. If the
     * constant does not exist, {@link Optional#absent} is returned. A common use case is for parsing
     * user input or falling back to a default enum constant. For example,
     * {@code Enums.getIfPresent(Country.class, countryInput).or(Country.DEFAULT);}
     *
     * @since 12.0
     */
    public static <T extends Enum<T>> Optional<T> getIfPresent(Class<T> enumClass, String value) {
        checkNotNull(enumClass);
        checkNotNull(value);
        return Platform.getEnumIfPresent(enumClass, value);
    }

    @GwtIncompatible("java.lang.ref.WeakReference")
    private static final Map<Class<? extends Enum<?>>, Map<String, WeakReference<? extends Enum<?>>>> enumConstantCache = new WeakHashMap<Class<? extends Enum<?>>, Map<String, WeakReference<? extends Enum<?>>>>();

    @GwtIncompatible("java.lang.ref.WeakReference")
    private static <T extends Enum<T>> Map<String, WeakReference<? extends Enum<?>>> populateCache(
            Class<T> enumClass) {
        Map<String, WeakReference<? extends Enum<?>>> result = new HashMap<String, WeakReference<? extends Enum<?>>>();
        for (T enumInstance : EnumSet.allOf(enumClass)) {
            result.put(enumInstance.name(), new WeakReference<Enum<?>>(enumInstance));
        }
        enumConstantCache.put(enumClass, result);
        return result;
    }

    @GwtIncompatible("java.lang.ref.WeakReference")
    static <T extends Enum<T>> Map<String, WeakReference<? extends Enum<?>>> getEnumConstants(Class<T> enumClass) {
        synchronized (enumConstantCache) {
            Map<String, WeakReference<? extends Enum<?>>> constants = enumConstantCache.get(enumClass);
            if (constants == null) {
                constants = populateCache(enumClass);
            }
            return constants;
        }
    }

    /**
     * Returns a converter that converts between strings and {@code enum} values of type
     * {@code enumClass} using {@link Enum#valueOf(Class, String)} and {@link Enum#name()}. The
     * converter will throw an {@code IllegalArgumentException} if the argument is not the name of
     * any enum constant in the specified enum.
     *
     * @since 16.0
     */
    public static <T extends Enum<T>> Converter<String, T> stringConverter(final Class<T> enumClass) {
        return new StringConverter<T>(enumClass);
    }

    private static final class StringConverter<T extends Enum<T>> extends Converter<String, T>
            implements Serializable {

        private final Class<T> enumClass;

        StringConverter(Class<T> enumClass) {
            this.enumClass = checkNotNull(enumClass);
        }

        @Override
        protected T doForward(String value) {
            return Enum.valueOf(enumClass, value);
        }

        @Override
        protected String doBackward(T enumValue) {
            return enumValue.name();
        }

        @Override
        public boolean equals(@Nullable Object object) {
            if (object instanceof StringConverter) {
                StringConverter<?> that = (StringConverter<?>) object;
                return this.enumClass.equals(that.enumClass);
            }
            return false;
        }

        @Override
        public int hashCode() {
            return enumClass.hashCode();
        }

        @Override
        public String toString() {
            return "Enums.stringConverter(" + enumClass.getName() + ".class)";
        }

        private static final long serialVersionUID = 0L;
    }
}