MapProviderFactory.java

/*
 * Copyright (C) 2014 The Dagger 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 dagger.internal;

import javax.inject.Provider;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;

import static dagger.internal.DaggerCollections.newLinkedHashMapWithExpectedSize;
import static java.util.Collections.unmodifiableMap;

/**
 * A {@link Factory} implementation used to implement {@link Map} bindings. This factory returns a
 * {@code Map<K, Provider<V>>} when calling {@link #get} (as specified by {@link Factory}).
 *
 * @author Chenying Hou
 * @since 2.0
 */
public final class MapProviderFactory<K, V> implements Factory<Map<K, Provider<V>>> {
    private static final MapProviderFactory<Object, Object> EMPTY =
        new MapProviderFactory<Object, Object>(Collections.<Object, Provider<Object>>emptyMap());

    private final Map<K, Provider<V>> contributingMap;

    /**
     * Returns a new {@link Builder}
     */
    public static <K, V> Builder<K, V> builder(int size) {
        return new Builder<K, V>(size);
    }

    /**
     * Returns a factory of an empty map.
     */
    @SuppressWarnings("unchecked") // safe contravariant cast
    public static <K, V> MapProviderFactory<K, V> empty() {
        return (MapProviderFactory<K, V>) EMPTY;
    }

    private MapProviderFactory(Map<K, Provider<V>> contributingMap) {
        this.contributingMap = unmodifiableMap(contributingMap);
    }

    /**
     * Returns a {@code Map<K, Provider<V>>} whose iteration order is that of the elements
     * given by each of the providers, which are invoked in the order given at creation.
     */
    @Override
    public Map<K, Provider<V>> get() {
        return this.contributingMap;
    }

    /**
     * A builder to help build the {@link MapProviderFactory}
     */
    public static final class Builder<K, V> {
        private final LinkedHashMap<K, Provider<V>> mapBuilder;

        private Builder(int size) {
            // TODO(user): consider which way to initialize mapBuilder is better
            this.mapBuilder = newLinkedHashMapWithExpectedSize(size);
        }

        /**
         * Returns a new {@link MapProviderFactory}
         */
        public MapProviderFactory<K, V> build() {
            return new MapProviderFactory<K, V>(this.mapBuilder);
        }

        /**
         * Associate k with providerOfValue in {@code Builder}
         */
        public Builder<K, V> put(K key, Provider<V> providerOfValue) {
            if (key == null) {
                throw new NullPointerException("The key is null");
            }
            if (providerOfValue == null) {
                throw new NullPointerException("The provider of the value is null");
            }

            this.mapBuilder.put(key, providerOfValue);
            return this;
        }
    }
}