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 /** 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 033 public 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 }