    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    }