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A fast dependency injector for Android and Java.
There is a newer version: 2.52
/*
 * Copyright (C) 2019 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.codegen.extension;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.ArrayList;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Optional;
import java.util.stream.Collector;
import javax.annotation.Nullable;

/**
 * A copy of {@link com.google.common.collect.MoreCollectors} to avoid issues with the '-android'
 * variant of Guava. See b/68008628
 */
public final class DaggerCollectors {

  private static final Collector> TO_OPTIONAL =
      Collector.of(
          ToOptionalState::new,
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}. The returned
   * collector throws an {@code IllegalArgumentException} if the stream consists of two or more
   * elements, and a {@code NullPointerException} if the stream consists of exactly one element,
   * which is null.
   */
  @SuppressWarnings("unchecked")
  public static  Collector> toOptional() {
    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

  private static final Collector ONLY_ELEMENT =
      Collector.of(
          ToOptionalState::new,
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),
          ToOptionalState::combine,
          state -> {
            Object result = state.getElement();
            return (result == NULL_PLACEHOLDER) ? null : result;
          },
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that takes a stream containing exactly one element and returns that element. The
   * returned collector throws an {@code IllegalArgumentException} if the stream consists of two or
   * more elements, and a {@code NoSuchElementException} if the stream is empty.
   */
  @SuppressWarnings("unchecked")
  public static  Collector onlyElement() {
    return (Collector) ONLY_ELEMENT;
  }

  private static final class ToOptionalState {
    static final int MAX_EXTRAS = 4;

    @Nullable Object element;
    @Nullable List