src/com/google/common/collect/MutableClassToInstanceMap.java

/*
 * Copyright (C) 2007 Google Inc.
 *
 * 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 java.util.HashMap;
import java.util.Map;

/**
 * A mutable class-to-instance map backed by an arbitrary user-provided map.
 * See also {@link ImmutableClassToInstanceMap}.
 *
 * @author Kevin Bourrillion
 */
public final class MutableClassToInstanceMap<B>
    extends ConstrainedMap<Class<? extends B>, B>
    implements ClassToInstanceMap<B> {

  /**
   * Returns a new {@code MutableClassToInstanceMap} instance backed by a {@link
   * HashMap} using the default initial capacity and load factor.
   */
  public static <B> MutableClassToInstanceMap<B> create() {
    return new MutableClassToInstanceMap<B>(
        new HashMap<Class<? extends B>, B>());
  }

  /**
   * Returns a new {@code MutableClassToInstanceMap} instance backed by a given
   * empty {@code backingMap}. The caller surrenders control of the backing map,
   * and thus should not allow any direct references to it to remain accessible.
   */
  public static <B> MutableClassToInstanceMap<B> create(
      Map<Class<? extends B>, B> backingMap) {
    return new MutableClassToInstanceMap<B>(backingMap);
  }

  private MutableClassToInstanceMap(Map<Class<? extends B>, B> delegate) {
    super(delegate, VALUE_CAN_BE_CAST_TO_KEY);
  }

  private static final MapConstraint<Class<?>, Object> VALUE_CAN_BE_CAST_TO_KEY
      = new MapConstraint<Class<?>, Object>() {
    public void checkKeyValue(Class<?> key, Object value) {
      cast(key, value);
    }
  };

  public <T extends B> T putInstance(Class<T> type, T value) {
    return cast(type, put(type, value));
  }

  public <T extends B> T getInstance(Class<T> type) {
    return cast(type, get(type));
  }

  // Default access so that ImmutableClassToInstanceMap can share it
  static <B, T extends B> T cast(Class<T> type, B value) {
    // TODO: this should eventually use common.primitives.Primitives.wrap()
    return wrap(type).cast(value);
  }

  // safe because both Long.class and long.class are of type Class<Long>
  @SuppressWarnings("unchecked")
  private static <T> Class<T> wrap(Class<T> c) {
    return c.isPrimitive() ? (Class<T>) PRIMITIVES_TO_WRAPPERS.get(c) : c;
  }

  private static final Map<Class<?>, Class<?>> PRIMITIVES_TO_WRAPPERS
      = new ImmutableMap.Builder<Class<?>, Class<?>>()
      .put(boolean.class, Boolean.class)
      .put(byte.class, Byte.class)
      .put(char.class, Character.class)
      .put(double.class, Double.class)
      .put(float.class, Float.class)
      .put(int.class, Integer.class)
      .put(long.class, Long.class)
      .put(short.class, Short.class)
      .put(void.class, Void.class)
      .build();
}