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
17 package com.google.common.reflect;
18
19 import com.google.common.annotations.Beta;
20
21 import java.util.Map;
22
23 import 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
48 public 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 }