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001    /*
002     * Copyright (C) 2011 The Guava Authors
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     * http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    
017    package com.google.common.base;
018    
019    import static com.google.common.base.Preconditions.checkNotNull;
020    
021    import com.google.common.annotations.Beta;
022    import com.google.common.annotations.GwtCompatible;
023    
024    import java.io.Serializable;
025    
026    import javax.annotation.Nullable;
027    
028    /**
029     * Utility methods for working with {@link Enum} instances.
030     *
031     * @author Steve McKay
032     *
033     * @since 9.0
034     */
035    @GwtCompatible
036    @Beta
037    public final class Enums {
038    
039      private Enums() {}
040    
041      /**
042       * Returns a {@link Function} that maps an {@link Enum} name to the associated
043       * {@code Enum} constant. The {@code Function} will return {@code null} if the
044       * {@code Enum} constant does not exist.
045       *
046       * @param enumClass the {@link Class} of the {@code Enum} declaring the
047       *     constant values.
048       */
049      public static <T extends Enum<T>> Function<String, T> valueOfFunction(Class<T> enumClass) {
050        return new ValueOfFunction<T>(enumClass);
051      }
052    
053      /**
054       * {@link Function} that maps an {@link Enum} name to the associated
055       * constant, or {@code null} if the constant does not exist.
056       */
057      private static final class ValueOfFunction<T extends Enum<T>> implements
058          Function<String, T>, Serializable {
059    
060        private final Class<T> enumClass;
061    
062        private ValueOfFunction(Class<T> enumClass) {
063          this.enumClass = checkNotNull(enumClass);
064        }
065    
066        @Override
067        public T apply(String value) {
068          try {
069            return Enum.valueOf(enumClass, value);
070          } catch (IllegalArgumentException e) {
071            return null;
072          }
073        }
074    
075        @Override public boolean equals(@Nullable Object obj) {
076          return obj instanceof ValueOfFunction &&
077              enumClass.equals(((ValueOfFunction) obj).enumClass);
078        }
079    
080        @Override public int hashCode() {
081          return enumClass.hashCode();
082        }
083    
084        @Override public String toString() {
085          return "Enums.valueOf(" + enumClass + ")";
086        }
087    
088        private static final long serialVersionUID = 0;
089      }
090    }