1/*
2 * Copyright (C) 2012 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.reflect;
18
19import com.google.common.annotations.Beta;
20
21import java.util.Map;
22
23import javax.annotation.Nullable;
24
25/**
26 * A map, each entry of which maps a {@link TypeToken} to an instance of that type.
27 * In addition to implementing {@code Map}, the additional type-safe operations
28 * {@link #putInstance} and {@link #getInstance} are available.
29 *
30 * <p>Generally, implementations don't support {@link #put} and {@link #putAll}
31 * because there is no way to check an object at runtime to be an instance of a
32 * {@link TypeToken}. Instead, caller should use the type safe {@link #putInstance}.
33 *
34 * <p>Also, if caller suppresses unchecked warnings and passes in an {@code Iterable<String>}
35 * for type {@code Iterable<Integer>}, the map won't be able to detect and throw type error.
36 *
37 * <p>Like any other {@code Map<Class, Object>}, this map may contain entries
38 * for primitive types, and a primitive type and its corresponding wrapper type
39 * may map to different values.
40 *
41 * @param <B> the common supertype that all entries must share; often this is
42 *     simply {@link Object}
43 *
44 * @author Ben Yu
45 * @since 13.0
46 */
47@Beta
48public interface TypeToInstanceMap<B> extends Map<TypeToken<? extends B>, B>  {
49
50  /**
51   * Returns the value the specified class is mapped to, or {@code null} if no
52   * entry for this class is present. This will only return a value that was
53   * bound to this specific class, not a value that may have been bound to a
54   * subtype.
55   *
56   * <p>{@code getInstance(Foo.class)} is equivalent to
57   * {@code getInstance(TypeToken.of(Foo.class))}.
58   */
59  @Nullable
60  <T extends B> T getInstance(Class<T> type);
61
62  /**
63   * Maps the specified class to the specified value. Does <i>not</i> associate
64   * this value with any of the class's supertypes.
65   *
66   * <p>{@code putInstance(Foo.class, foo)} is equivalent to
67   * {@code putInstance(TypeToken.of(Foo.class), foo)}.
68   *
69   * @return the value previously associated with this class (possibly {@code null}),
70   *         or {@code null} if there was no previous entry.
71   */
72  @Nullable
73  <T extends B> T putInstance(Class<T> type, @Nullable T value);
74
75  /**
76   * Returns the value the specified type is mapped to, or {@code null} if no
77   * entry for this type is present. This will only return a value that was
78   * bound to this specific type, not a value that may have been bound to a subtype.
79   */
80  @Nullable
81  <T extends B> T getInstance(TypeToken<T> type);
82
83  /**
84   * Maps the specified type to the specified value. Does <i>not</i> associate
85   * this value with any of the type's supertypes.
86   *
87   * @return the value previously associated with this type (possibly {@code null}),
88   *         or {@code null} if there was no previous entry.
89   */
90  @Nullable
91  <T extends B> T putInstance(TypeToken<T> type, @Nullable T value);
92}
93