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.
   */
  package org.apache.beam.runners.core;
  
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.values.PCollectionView;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * The interface to objects that provide side inputs. Particular implementations may read a side
   * input directly or use appropriate sorts of caching, etc.
   */
  public interface SideInputReader {
    /**
     * Returns the value of the given {@link PCollectionView} for the given {@link BoundedWindow}.
     *
     * <p>It is valid for a side input to be {@code null}. It is <i>not</i> valid for this to return
     * {@code null} for any other reason.
     */
    @Nullable
    <T> T get(PCollectionView<T> view, BoundedWindow window);
  
    /** Returns true if the given {@link PCollectionView} is valid for this reader. */
    <T> boolean contains(PCollectionView<T> view);
  
    /** Returns true if there are no side inputs in this reader. */
    boolean isEmpty();
  }
  