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
017package com.google.common.base;
018
019import static com.google.common.base.Preconditions.checkNotNull;
020
021import com.google.common.annotations.Beta;
022import com.google.common.annotations.GwtCompatible;
023
024/**
025 * Utility methods for working with {@link Enum} instances.
026 *
027 * @author smckay@google.com (Steve McKay)
028 *
029 * @since 9
030 */
031@GwtCompatible
032@Beta
033public final class Enums {
034
035  private Enums() {}
036
037  /**
038   * Returns a {@link Function} that maps an {@link Enum} name to the associated
039   * {@code Enum} constant. The {@code Function} will return {@code null} if the
040   * {@code Enum} constant does not exist.
041   *
042   * @param enumClass the {@link Class} of the {@code Enum} declaring the
043   *     constant values.
044   */
045  public static <T extends Enum<T>> Function<String, T> valueOfFunction(Class<T> enumClass) {
046    return new ValueOfFunction<T>(enumClass);
047  }
048
049  /**
050   * {@link Function} that maps an {@link Enum} name to the associated
051   * constant, or {@code null} if the constant does not exist.
052   */
053  private static final class ValueOfFunction<T extends Enum<T>> implements
054      Function<String, T> {
055
056    private final Class<T> enumClass;
057
058    private ValueOfFunction(Class<T> enumClass) {
059      this.enumClass = checkNotNull(enumClass);
060    }
061
062    @Override
063    public T apply(String value) {
064      try {
065        return Enum.valueOf(enumClass, value);
066      } catch (IllegalArgumentException e) {
067        return null;
068      }
069    }
070  }
071}