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  }