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
017package com.google.common.reflect;
018
019import com.google.common.annotations.Beta;
020
021import java.util.Map;
022
023import 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
048public 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}