1/*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.base;
18
19import static com.google.common.base.Preconditions.checkNotNull;
20
21import com.google.common.annotations.Beta;
22import com.google.common.annotations.GwtCompatible;
23
24import java.io.Serializable;
25
26import javax.annotation.Nullable;
27
28/**
29 * Utility methods for working with {@link Enum} instances.
30 *
31 * @author Steve McKay
32 *
33 * @since 9.0
34 */
35@GwtCompatible
36@Beta
37public final class Enums {
38
39  private Enums() {}
40
41  /**
42   * Returns a {@link Function} that maps an {@link Enum} name to the associated
43   * {@code Enum} constant. The {@code Function} will return {@code null} if the
44   * {@code Enum} constant does not exist.
45   *
46   * @param enumClass the {@link Class} of the {@code Enum} declaring the
47   *     constant values.
48   */
49  public static <T extends Enum<T>> Function<String, T> valueOfFunction(Class<T> enumClass) {
50    return new ValueOfFunction<T>(enumClass);
51  }
52
53  /**
54   * {@link Function} that maps an {@link Enum} name to the associated
55   * constant, or {@code null} if the constant does not exist.
56   */
57  private static final class ValueOfFunction<T extends Enum<T>> implements
58      Function<String, T>, Serializable {
59
60    private final Class<T> enumClass;
61
62    private ValueOfFunction(Class<T> enumClass) {
63      this.enumClass = checkNotNull(enumClass);
64    }
65
66    @Override
67    public T apply(String value) {
68      try {
69        return Enum.valueOf(enumClass, value);
70      } catch (IllegalArgumentException e) {
71        return null;
72      }
73    }
74
75    @Override public boolean equals(@Nullable Object obj) {
76      return obj instanceof ValueOfFunction &&
77          enumClass.equals(((ValueOfFunction) obj).enumClass);
78    }
79
80    @Override public int hashCode() {
81      return enumClass.hashCode();
82    }
83
84    @Override public String toString() {
85      return "Enums.valueOf(" + enumClass + ")";
86    }
87
88    private static final long serialVersionUID = 0;
89  }
90}
91