001/*
002 * Copyright (C) 2009 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 static com.google.common.base.Preconditions.checkNotNull;
020
021import com.google.common.annotations.GwtIncompatible;
022import com.google.common.primitives.Primitives;
023import com.google.errorprone.annotations.CanIgnoreReturnValue;
024import com.google.errorprone.annotations.DoNotCall;
025import com.google.errorprone.annotations.Immutable;
026import java.io.Serializable;
027import java.util.Map;
028import org.jspecify.annotations.NonNull;
029import org.jspecify.annotations.Nullable;
030
031/**
032 * A {@link ClassToInstanceMap} whose contents will never change, with many other important
033 * properties detailed at {@link ImmutableCollection}.
034 *
035 * @author Kevin Bourrillion
036 * @since 2.0
037 */
038@Immutable(containerOf = "B")
039@GwtIncompatible
040// TODO(b/278589132): Remove the redundant "@NonNull" on B once it's no longer required by J2KT.
041public final class ImmutableClassToInstanceMap<B>
042    extends ForwardingMap<Class<? extends @NonNull B>, B>
043    implements ClassToInstanceMap<B>, Serializable {
044
045  private static final ImmutableClassToInstanceMap<Object> EMPTY =
046      new ImmutableClassToInstanceMap<>(ImmutableMap.of());
047
048  /**
049   * Returns an empty {@code ImmutableClassToInstanceMap}.
050   *
051   * <p><b>Performance note:</b> the instance returned is a singleton.
052   *
053   * @since 19.0
054   */
055  @SuppressWarnings("unchecked")
056  public static <B> ImmutableClassToInstanceMap<B> of() {
057    return (ImmutableClassToInstanceMap<B>) EMPTY;
058  }
059
060  /**
061   * Returns an {@code ImmutableClassToInstanceMap} containing a single entry.
062   *
063   * @since 19.0
064   */
065  public static <B, T extends B> ImmutableClassToInstanceMap<B> of(Class<T> type, T value) {
066    return new ImmutableClassToInstanceMap<>(ImmutableMap.of(type, value));
067  }
068
069  /**
070   * Returns a new builder. The generated builder is equivalent to the builder created by the {@link
071   * Builder} constructor.
072   */
073  public static <B> Builder<B> builder() {
074    return new Builder<>();
075  }
076
077  /**
078   * A builder for creating immutable class-to-instance maps. Example:
079   *
080   * {@snippet :
081   * static final ImmutableClassToInstanceMap<Handler> HANDLERS =
082   *     new ImmutableClassToInstanceMap.Builder<Handler>()
083   *         .put(FooHandler.class, new FooHandler())
084   *         .put(BarHandler.class, new SubBarHandler())
085   *         .put(Handler.class, new QuuxHandler())
086   *         .build();
087   * }
088   *
089   * <p>After invoking {@link #build()} it is still possible to add more entries and build again.
090   * Thus each map generated by this builder will be a superset of any map generated before it.
091   *
092   * @since 2.0
093   */
094  public static final class Builder<B> {
095    /** Creates a new builder. */
096    public Builder() {}
097
098    private final ImmutableMap.Builder<Class<? extends B>, B> mapBuilder = ImmutableMap.builder();
099
100    /**
101     * Associates {@code key} with {@code value} in the built map. Duplicate keys are not allowed,
102     * and will cause {@link #build} to fail.
103     */
104    @CanIgnoreReturnValue
105    public <T extends B> Builder<B> put(Class<T> key, T value) {
106      mapBuilder.put(key, value);
107      return this;
108    }
109
110    /**
111     * Associates all of {@code map's} keys and values in the built map. Duplicate keys are not
112     * allowed, and will cause {@link #build} to fail.
113     *
114     * @throws NullPointerException if any key or value in {@code map} is null
115     * @throws ClassCastException if any value is not an instance of the type specified by its key
116     */
117    @CanIgnoreReturnValue
118    public <T extends B> Builder<B> putAll(Map<? extends Class<? extends T>, ? extends T> map) {
119      for (Entry<? extends Class<? extends T>, ? extends T> entry : map.entrySet()) {
120        Class<? extends T> key = entry.getKey();
121        T value = entry.getValue();
122        cast(key, value); // If we pass this result to `put` below, it upsets our nullness checker.
123        mapBuilder.put(key, value);
124      }
125      return this;
126    }
127
128    /**
129     * Returns a new immutable class-to-instance map containing the entries provided to this
130     * builder.
131     *
132     * @throws IllegalArgumentException if duplicate keys were added
133     */
134    public ImmutableClassToInstanceMap<B> build() {
135      ImmutableMap<Class<? extends B>, B> map = mapBuilder.buildOrThrow();
136      if (map.isEmpty()) {
137        return of();
138      } else {
139        return new ImmutableClassToInstanceMap<>(map);
140      }
141    }
142  }
143
144  /**
145   * Returns an immutable map containing the same entries as {@code map}. If {@code map} somehow
146   * contains entries with duplicate keys (for example, if it is a {@code SortedMap} whose
147   * comparator is not <i>consistent with equals</i>), the results of this method are undefined.
148   *
149   * <p><b>Note:</b> Despite what the method name suggests, if {@code map} is an {@code
150   * ImmutableClassToInstanceMap}, no copy will actually be performed.
151   *
152   * @throws NullPointerException if any key or value in {@code map} is null
153   * @throws ClassCastException if any value is not an instance of the type specified by its key
154   */
155  public static <B, S extends B> ImmutableClassToInstanceMap<B> copyOf(
156      Map<? extends Class<? extends S>, ? extends S> map) {
157    if (map instanceof ImmutableClassToInstanceMap) {
158      @SuppressWarnings("rawtypes") // JDT-based J2KT Java frontend does not permit the direct cast
159      Map rawMap = map;
160      @SuppressWarnings("unchecked") // covariant casts safe (unmodifiable)
161      ImmutableClassToInstanceMap<B> cast = (ImmutableClassToInstanceMap<B>) rawMap;
162      return cast;
163    }
164    return new Builder<B>().putAll(map).build();
165  }
166
167  private final ImmutableMap<Class<? extends B>, B> delegate;
168
169  private ImmutableClassToInstanceMap(ImmutableMap<Class<? extends B>, B> delegate) {
170    this.delegate = delegate;
171  }
172
173  @Override
174  protected Map<Class<? extends B>, B> delegate() {
175    return delegate;
176  }
177
178  @Override
179  public <T extends B> @Nullable T getInstance(Class<T> type) {
180    return cast(type, delegate.get(checkNotNull(type)));
181  }
182
183  /**
184   * Guaranteed to throw an exception and leave the map unmodified.
185   *
186   * @throws UnsupportedOperationException always
187   * @deprecated Unsupported operation.
188   */
189  @CanIgnoreReturnValue
190  @Deprecated
191  @Override
192  @DoNotCall("Always throws UnsupportedOperationException")
193  public <T extends B> @Nullable T putInstance(Class<T> type, T value) {
194    throw new UnsupportedOperationException();
195  }
196
197  @CanIgnoreReturnValue
198  private static <T> @Nullable T cast(Class<T> type, @Nullable Object value) {
199    return Primitives.wrap(type).cast(value);
200  }
201
202  Object readResolve() {
203    return isEmpty() ? of() : this;
204  }
205}