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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.reflect.Field;
import javax.annotation.Nullable;
/**
* Utility methods for working with {@link Enum} instances.
*
* @author Steve McKay
*
* @since 9.0
*/
@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 a {@link Function} that maps an {@link Enum} name to the associated
* {@code Enum} constant. The {@code Function} will return {@code null} if the
* {@code Enum} constant does not exist.
*
* @param enumClass the {@link Class} of the {@code Enum} declaring the
* constant values.
*/
public static <T extends Enum<T>> Function<String, T> valueOfFunction(Class<T> enumClass) {
return new ValueOfFunction<T>(enumClass);
}
/**
* A {@link Function} that maps an {@link Enum} name to the associated
* constant, or {@code null} if the constant does not exist.
*/
private static final class ValueOfFunction<T extends Enum<T>>
implements Function<String, T>, Serializable {
private final Class<T> enumClass;
private ValueOfFunction(Class<T> enumClass) {
this.enumClass = checkNotNull(enumClass);
}
@Override
public T apply(String value) {
try {
return Enum.valueOf(enumClass, value);
} catch (IllegalArgumentException e) {
return null;
}
}
@Override public boolean equals(@Nullable Object obj) {
return obj instanceof ValueOfFunction &&
enumClass.equals(((ValueOfFunction) obj).enumClass);
}
@Override public int hashCode() {
return enumClass.hashCode();
}
@Override public String toString() {
return "Enums.valueOf(" + enumClass + ")";
}
private static final long serialVersionUID = 0;
}
/**
* 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);
try {
return Optional.of(Enum.valueOf(enumClass, value));
} catch (IllegalArgumentException iae) {
return Optional.absent();
}
}
}
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