content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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.
   */
  /**
   * Defines {@link org.apache.beam.sdk.values.PCollection} and other classes for representing data in
   * a {@link org.apache.beam.sdk.Pipeline}.
   *
   * <p>In particular, see these collection abstractions:
   *
   * <ul>
   *   <li>{@link org.apache.beam.sdk.values.PCollection} - an immutable collection of values of type
   *       {@code T} and the main representation for data in Beam.
   *   <li>{@link org.apache.beam.sdk.values.PCollectionView} - an immutable view of a {@link
   *       org.apache.beam.sdk.values.PCollection} that can be accessed as a side input of a {@link
   *       org.apache.beam.sdk.transforms.ParDo} {@link org.apache.beam.sdk.transforms.PTransform}.
   *   <li>{@link org.apache.beam.sdk.values.PCollectionTuple} - a heterogeneous tuple of {@link
   *       org.apache.beam.sdk.values.PCollection PCollections} used in cases where a {@link
   *       org.apache.beam.sdk.transforms.PTransform} takes or returns multiple {@link
   *       org.apache.beam.sdk.values.PCollection PCollections}.
   *   <li>{@link org.apache.beam.sdk.values.PCollectionList} - a homogeneous list of {@link
   *       org.apache.beam.sdk.values.PCollection PCollections} used, for example, as input to {@link
   *       org.apache.beam.sdk.transforms.Flatten}.
   * </ul>
   *
   * <p>And these classes for individual values play particular roles in Beam:
   *
   * <ul>
   *   <li>{@link org.apache.beam.sdk.values.KV} - a key/value pair that is used by keyed transforms,
   *       most notably {@link org.apache.beam.sdk.transforms.GroupByKey}.
   *   <li>{@link org.apache.beam.sdk.values.TimestampedValue} - a timestamp/value pair that is used
   *       for windowing and handling out-of-order data in streaming execution.
   * </ul>
   *
   * <p>For further details, see the documentation for each class in this package.
   */
  @DefaultAnnotation(NonNull.class)
  package org.apache.beam.sdk.values;
  
  import edu.umd.cs.findbugs.annotations.DefaultAnnotation;
  import org.checkerframework.checker.nullness.qual.NonNull;
  