guava/src/com/google/common/collect/ClassToInstanceMap.java

/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Map;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A map, each entry of which maps a Java <a href="http://tinyurl.com/2cmwkz">raw type</a> to an
 * instance of that type. In addition to implementing {@code Map}, the additional type-safe
 * operations {@link #putInstance} and {@link #getInstance} are available.
 *
 * <p>Like any other {@code Map<Class, Object>}, this map may contain entries for primitive types,
 * and a primitive type and its corresponding wrapper type may map to different values.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#classtoinstancemap"> {@code
 * ClassToInstanceMap}</a>.
 *
 * <p>To map a generic type to an instance of that type, use {@link
 * com.google.common.reflect.TypeToInstanceMap} instead.
 *
 * @param <B> the common supertype that all entries must share; often this is simply {@link Object}
 * @author Kevin Bourrillion
 * @since 2.0
 */
@GwtCompatible
public interface ClassToInstanceMap<B> extends Map<Class<? extends B>, B> {
  /**
   * Returns the value the specified class is mapped to, or {@code null} if no entry for this class
   * is present. This will only return a value that was bound to this specific class, not a value
   * that may have been bound to a subtype.
   */
  <T extends B> T getInstance(Class<T> type);

  /**
   * Maps the specified class to the specified value. Does <i>not</i> associate this value with any
   * of the class's supertypes.
   *
   * @return the value previously associated with this class (possibly {@code null}), or {@code
   *     null} if there was no previous entry.
   */
  @CanIgnoreReturnValue
  <T extends B> T putInstance(Class<T> type, @Nullable T value);
}