Java tutorial
/* * 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 com.google.common.primitives.Primitives; import java.io.Serializable; import java.util.Map; import javax.annotation.Nullable; /** * A {@link ClassToInstanceMap} whose contents will never change, with many * other important properties detailed at {@link ImmutableCollection}. * * @author Kevin Bourrillion * @since 2.0 */ public final class ImmutableClassToInstanceMap<B> extends ForwardingMap<Class<? extends B>, B> implements ClassToInstanceMap<B>, Serializable { private static final ImmutableClassToInstanceMap<Object> EMPTY = new ImmutableClassToInstanceMap<Object>( ImmutableMap.<Class<?>, Object>of()); /** * Returns an empty {@code ImmutableClassToInstanceMap}. * * @since 19.0 */ @SuppressWarnings("unchecked") public static <B> ImmutableClassToInstanceMap<B> of() { return (ImmutableClassToInstanceMap<B>) EMPTY; } /** * Returns an {@code ImmutableClassToInstanceMap} containing a single entry. * * @since 19.0 */ public static <B, T extends B> ImmutableClassToInstanceMap<B> of(Class<T> type, T value) { ImmutableMap<Class<? extends B>, B> map = ImmutableMap.<Class<? extends B>, B>of(type, value); return new ImmutableClassToInstanceMap<B>(map); } /** * 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> {@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 */ 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() { ImmutableMap<Class<? extends B>, B> map = mapBuilder.build(); if (map.isEmpty()) { return of(); } else { return new ImmutableClassToInstanceMap<B>(map); } } } /** * 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(); } Object readResolve() { return isEmpty() ? of() : this; } }