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
017package com.google.common.reflect;
018
019import com.google.common.annotations.Beta;
020import com.google.common.collect.ForwardingMap;
021import com.google.common.collect.ImmutableMap;
022
023import 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
033public 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   * <p>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}