001 /*
002 * Copyright (C) 2012 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.reflect;
018
019 import com.google.common.annotations.Beta;
020
021 import java.util.Map;
022
023 import javax.annotation.Nullable;
024
025 /**
026 * A map, each entry of which maps a {@link TypeToken} to an instance of that type.
027 * In addition to implementing {@code Map}, the additional type-safe operations
028 * {@link #putInstance} and {@link #getInstance} are available.
029 *
030 * <p>Generally, implementations don't support {@link #put} and {@link #putAll}
031 * because there is no way to check an object at runtime to be an instance of a
032 * {@link TypeToken}. Instead, caller should use the type safe {@link #putInstance}.
033 *
034 * <p>Also, if caller suppresses unchecked warnings and passes in an {@code Iterable<String>}
035 * for type {@code Iterable<Integer>}, the map won't be able to detect and throw type error.
036 *
037 * <p>Like any other {@code Map<Class, Object>}, this map may contain entries
038 * for primitive types, and a primitive type and its corresponding wrapper type
039 * may map to different values.
040 *
041 * @param <B> the common supertype that all entries must share; often this is
042 * simply {@link Object}
043 *
044 * @author Ben Yu
045 * @since 13.0
046 */
047 @Beta
048 public interface TypeToInstanceMap<B> extends Map<TypeToken<? extends B>, B> {
049
050 /**
051 * Returns the value the specified class is mapped to, or {@code null} if no
052 * entry for this class is present. This will only return a value that was
053 * bound to this specific class, not a value that may have been bound to a
054 * subtype.
055 *
056 * <p>{@code getInstance(Foo.class)} is equivalent to
057 * {@code getInstance(TypeToken.of(Foo.class))}.
058 */
059 @Nullable
060 <T extends B> T getInstance(Class<T> type);
061
062 /**
063 * Maps the specified class to the specified value. Does <i>not</i> associate
064 * this value with any of the class's supertypes.
065 *
066 * <p>{@code putInstance(Foo.class, foo)} is equivalent to
067 * {@code putInstance(TypeToken.of(Foo.class), foo)}.
068 *
069 * @return the value previously associated with this class (possibly {@code null}),
070 * or {@code null} if there was no previous entry.
071 */
072 @Nullable
073 <T extends B> T putInstance(Class<T> type, @Nullable T value);
074
075 /**
076 * Returns the value the specified type is mapped to, or {@code null} if no
077 * entry for this type is present. This will only return a value that was
078 * bound to this specific type, not a value that may have been bound to a subtype.
079 */
080 @Nullable
081 <T extends B> T getInstance(TypeToken<T> type);
082
083 /**
084 * Maps the specified type to the specified value. Does <i>not</i> associate
085 * this value with any of the type's supertypes.
086 *
087 * @return the value previously associated with this type (possibly {@code null}),
088 * or {@code null} if there was no previous entry.
089 */
090 @Nullable
091 <T extends B> T putInstance(TypeToken<T> type, @Nullable T value);
092 }