001 /*
002 * Copyright (C) 2012 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
017 package com.google.common.reflect;
018
019 import com.google.common.annotations.Beta;
020 import com.google.common.collect.ForwardingMap;
021 import com.google.common.collect.ImmutableMap;
022
023 import java.util.Map;
024
025 /**
026 * A type-to-instance map backed by an {@link ImmutableMap}. See also {@link
027 * MutableTypeToInstanceMap}.
028 *
029 * @author Ben Yu
030 * @since 13.0
031 */
032 @Beta
033 public final class ImmutableTypeToInstanceMap<B> extends ForwardingMap<TypeToken<? extends B>, B>
034 implements TypeToInstanceMap<B> {
035
036 /** Returns an empty type to instance map. */
037 public static <B> ImmutableTypeToInstanceMap<B> of() {
038 return new ImmutableTypeToInstanceMap<B>(ImmutableMap.<TypeToken<? extends B>, B>of());
039 }
040
041 /** Returns a new builder. */
042 public static <B> Builder<B> builder() {
043 return new Builder<B>();
044 }
045
046 /**
047 * A builder for creating immutable type-to-instance maps. Example:
048 * <pre> {@code
049 *
050 * static final ImmutableTypeToInstanceMap<Handler<?>> HANDLERS =
051 * ImmutableTypeToInstanceMap.<Handler<?>>builder()
052 * .put(new TypeToken<Handler<Foo>>() {}, new FooHandler())
053 * .put(new TypeToken<Handler<Bar>>() {}, new SubBarHandler())
054 * .build();}</pre>
055 *
056 * After invoking {@link #build()} it is still possible to add more entries
057 * and build again. Thus each map generated by this builder will be a superset
058 * of any map generated before it.
059 *
060 * @since 13.0
061 */
062 @Beta
063 public static final class Builder<B> {
064 private final ImmutableMap.Builder<TypeToken<? extends B>, B> mapBuilder
065 = ImmutableMap.builder();
066
067 private Builder() {}
068
069 /**
070 * Associates {@code key} with {@code value} in the built map. Duplicate
071 * keys are not allowed, and will cause {@link #build} to fail.
072 */
073 public <T extends B> Builder<B> put(Class<T> key, T value) {
074 mapBuilder.put(TypeToken.of(key), value);
075 return this;
076 }
077
078 /**
079 * Associates {@code key} with {@code value} in the built map. Duplicate
080 * keys are not allowed, and will cause {@link #build} to fail.
081 */
082 public <T extends B> Builder<B> put(TypeToken<T> key, T value) {
083 mapBuilder.put(key.rejectTypeVariables(), value);
084 return this;
085 }
086
087 /**
088 * Returns a new immutable type-to-instance map containing the entries
089 * provided to this builder.
090 *
091 * @throws IllegalArgumentException if duplicate keys were added
092 */
093 public ImmutableTypeToInstanceMap<B> build() {
094 return new ImmutableTypeToInstanceMap<B>(mapBuilder.build());
095 }
096 }
097
098 private final ImmutableMap<TypeToken<? extends B>, B> delegate;
099
100 private ImmutableTypeToInstanceMap(ImmutableMap<TypeToken<? extends B>, B> delegate) {
101 this.delegate = delegate;
102 }
103
104 @Override public <T extends B> T getInstance(TypeToken<T> type) {
105 return trustedGet(type.rejectTypeVariables());
106 }
107
108 /**
109 * Guaranteed to throw an exception and leave the map unmodified.
110 *
111 * @throws UnsupportedOperationException always
112 */
113 @Override public <T extends B> T putInstance(TypeToken<T> type, T value) {
114 throw new UnsupportedOperationException();
115 }
116
117 @Override public <T extends B> T getInstance(Class<T> type) {
118 return trustedGet(TypeToken.of(type));
119 }
120
121 /**
122 * Guaranteed to throw an exception and leave the map unmodified.
123 *
124 * @throws UnsupportedOperationException always
125 */
126 @Override public <T extends B> T putInstance(Class<T> type, T value) {
127 throw new UnsupportedOperationException();
128 }
129
130 @Override protected Map<TypeToken<? extends B>, B> delegate() {
131 return delegate;
132 }
133
134 @SuppressWarnings("unchecked") // value could not get in if not a T
135 private <T extends B> T trustedGet(TypeToken<T> type) {
136 return (T) delegate.get(type);
137 }
138 }