EaglerForge/sources/main/java/com/google/common/collect/ImmutableClassToInstanceMap.java

/*
 * Copyright (C) 2009 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 static com.google.common.base.Preconditions.checkNotNull;

import java.io.Serializable;
import java.util.Map;

import javax.annotation.Nullable;

import com.google.common.primitives.Primitives;

/**
 * A class-to-instance map backed by an {@link ImmutableMap}. See also
 * {@link MutableClassToInstanceMap}.
 *
 * @author Kevin Bourrillion
 * @since 2.0 (imported from Google Collections Library)
 */
public final class ImmutableClassToInstanceMap<B> extends ForwardingMap<Class<? extends B>, B>
		implements ClassToInstanceMap<B>, Serializable {

	/**
	 * Returns a new builder. The generated builder is equivalent to the builder
	 * created by the {@link Builder} constructor.
	 */
	public static <B> Builder<B> builder() {
		return new Builder<B>();
	}

	/**
	 * A builder for creating immutable class-to-instance maps. Example:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	static final ImmutableClassToInstanceMap<Handler> HANDLERS = new ImmutableClassToInstanceMap.Builder<Handler>()
	 * 			.put(FooHandler.class, new FooHandler()).put(BarHandler.class, new SubBarHandler())
	 * 			.put(Handler.class, new QuuxHandler()).build();
	 * }
	 * </pre>
	 *
	 * <p>
	 * After invoking {@link #build()} it is still possible to add more entries and
	 * build again. Thus each map generated by this builder will be a superset of
	 * any map generated before it.
	 *
	 * @since 2.0 (imported from Google Collections Library)
	 */
	public static final class Builder<B> {
		private final ImmutableMap.Builder<Class<? extends B>, B> mapBuilder = ImmutableMap.builder();

		/**
		 * Associates {@code key} with {@code value} in the built map. Duplicate keys
		 * are not allowed, and will cause {@link #build} to fail.
		 */
		public <T extends B> Builder<B> put(Class<T> key, T value) {
			mapBuilder.put(key, value);
			return this;
		}

		/**
		 * Associates all of {@code map's} keys and values in the built map. Duplicate
		 * keys are not allowed, and will cause {@link #build} to fail.
		 *
		 * @throws NullPointerException if any key or value in {@code map} is null
		 * @throws ClassCastException   if any value is not an instance of the type
		 *                              specified by its key
		 */
		public <T extends B> Builder<B> putAll(Map<? extends Class<? extends T>, ? extends T> map) {
			for (Entry<? extends Class<? extends T>, ? extends T> entry : map.entrySet()) {
				Class<? extends T> type = entry.getKey();
				T value = entry.getValue();
				mapBuilder.put(type, cast(type, value));
			}
			return this;
		}

		private static <B, T extends B> T cast(Class<T> type, B value) {
			return Primitives.wrap(type).cast(value);
		}

		/**
		 * Returns a new immutable class-to-instance map containing the entries provided
		 * to this builder.
		 *
		 * @throws IllegalArgumentException if duplicate keys were added
		 */
		public ImmutableClassToInstanceMap<B> build() {
			return new ImmutableClassToInstanceMap<B>(mapBuilder.build());
		}
	}

	/**
	 * Returns an immutable map containing the same entries as {@code map}. If
	 * {@code map} somehow contains entries with duplicate keys (for example, if it
	 * is a {@code SortedMap} whose comparator is not <i>consistent with
	 * equals</i>), the results of this method are undefined.
	 *
	 * <p>
	 * <b>Note:</b> Despite what the method name suggests, if {@code map} is an
	 * {@code ImmutableClassToInstanceMap}, no copy will actually be performed.
	 *
	 * @throws NullPointerException if any key or value in {@code map} is null
	 * @throws ClassCastException   if any value is not an instance of the type
	 *                              specified by its key
	 */
	public static <B, S extends B> ImmutableClassToInstanceMap<B> copyOf(
			Map<? extends Class<? extends S>, ? extends S> map) {
		if (map instanceof ImmutableClassToInstanceMap) {
			@SuppressWarnings("unchecked") // covariant casts safe (unmodifiable)
			// Eclipse won't compile if we cast to the parameterized type.
			ImmutableClassToInstanceMap<B> cast = (ImmutableClassToInstanceMap) map;
			return cast;
		}
		return new Builder<B>().putAll(map).build();
	}

	private final ImmutableMap<Class<? extends B>, B> delegate;

	private ImmutableClassToInstanceMap(ImmutableMap<Class<? extends B>, B> delegate) {
		this.delegate = delegate;
	}

	@Override
	protected Map<Class<? extends B>, B> delegate() {
		return delegate;
	}

	@Override
	@SuppressWarnings("unchecked") // value could not get in if not a T
	@Nullable
	public <T extends B> T getInstance(Class<T> type) {
		return (T) delegate.get(checkNotNull(type));
	}

	/**
	 * Guaranteed to throw an exception and leave the map unmodified.
	 *
	 * @throws UnsupportedOperationException always
	 * @deprecated Unsupported operation.
	 */
	@Deprecated
	@Override
	public <T extends B> T putInstance(Class<T> type, T value) {
		throw new UnsupportedOperationException();
	}
}