001/* 002 * Copyright (C) 2007 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.collect; 018 019import com.google.common.annotations.GwtCompatible; 020import com.google.errorprone.annotations.CanIgnoreReturnValue; 021import com.google.errorprone.annotations.DoNotMock; 022import java.util.Map; 023import javax.annotation.CheckForNull; 024 025/** 026 * A map, each entry of which maps a Java <a href="http://tinyurl.com/2cmwkz">raw type</a> to an 027 * instance of that type. In addition to implementing {@code Map}, the additional type-safe 028 * operations {@link #putInstance} and {@link #getInstance} are available. 029 * 030 * <p>Like any other {@code Map<Class, Object>}, this map may contain entries for primitive types, 031 * and a primitive type and its corresponding wrapper type may map to different values. 032 * 033 * <p>This class's support for {@code null} requires some explanation: From release 31.0 onward, 034 * Guava specifies the nullness of its types through annotations. In the case of {@code 035 * ClassToInstanceMap}, it specifies that both the key and value types are restricted to 036 * non-nullable types. This specification is reasonable for <i>keys</i>, which must be non-null 037 * classes. This is in contrast to the specification for <i>values</i>: Null values <i>are</i> 038 * supported by the implementation {@link MutableClassToInstanceMap}, even though that 039 * implementation and this interface specify otherwise. Thus, if you use a nullness checker, you can 040 * safely suppress any warnings it produces when you write null values into a {@code 041 * MutableClassToInstanceMap}. Just be sure to be prepared for null values when reading from it, 042 * since nullness checkers will assume that vaules are non-null then, too. 043 * 044 * <p>See the Guava User Guide article on <a href= 045 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#classtoinstancemap">{@code 046 * ClassToInstanceMap}</a>. 047 * 048 * <p>To map a generic type to an instance of that type, use {@link 049 * com.google.common.reflect.TypeToInstanceMap} instead. 050 * 051 * @param <B> the common supertype that all entries must share; often this is simply {@link Object} 052 * @author Kevin Bourrillion 053 * @since 2.0 054 */ 055@DoNotMock("Use ImmutableClassToInstanceMap or MutableClassToInstanceMap") 056@GwtCompatible 057@ElementTypesAreNonnullByDefault 058// If we ever support non-null projections (https://github.com/jspecify/jspecify/issues/86), we 059// we might annotate this as... 060// ClassToInstanceMap<B extends @Nullable Object> extends Map<Class<? extends @Nonnull B>, B> 061// ...and change its methods similarly (<T extends @Nonnull B> or Class<@Nonnull T>). 062public interface ClassToInstanceMap<B> extends Map<Class<? extends B>, B> { 063 /** 064 * Returns the value the specified class is mapped to, or {@code null} if no entry for this class 065 * is present. This will only return a value that was bound to this specific class, not a value 066 * that may have been bound to a subtype. 067 */ 068 @CheckForNull 069 <T extends B> T getInstance(Class<T> type); 070 071 /** 072 * Maps the specified class to the specified value. Does <i>not</i> associate this value with any 073 * of the class's supertypes. 074 * 075 * @return the value previously associated with this class (possibly {@code null}), or {@code 076 * null} if there was no previous entry. 077 */ 078 @CanIgnoreReturnValue 079 @CheckForNull 080 <T extends B> T putInstance(Class<T> type, T value); 081}