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.sdk.util.common;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Observer;
  import org.apache.beam.sdk.annotations.Internal;
  
  /**
   * An abstract class used for iterables that notify observers about size in bytes of their elements,
   * as they are being iterated over.
   *
   * @param <V> the type of elements returned by this iterable
   * @param <InputT> type type of iterator returned by this iterable
   */
  @Internal
  public abstract class ElementByteSizeObservableIterable<
          V, InputT extends ElementByteSizeObservableIterator<V>>
      implements Iterable<V> {
    private List<Observer> observers = new ArrayList<>();
  
    /** Derived classes override this method to return an iterator for this iterable. */
    protected abstract InputT createIterator();
  
    /**
     * Sets the observer, which will observe the iterator returned in the next call to iterator()
     * method. Future calls to iterator() won't be observed, unless an observer is set again.
     */
    public void addObserver(Observer observer) {
      observers.add(observer);
    }
  
    /**
     * Returns a new iterator for this iterable. If an observer was set in a previous call to
     * setObserver(), it will observe the iterator returned.
     */
    @Override
    public InputT iterator() {
      InputT iterator = createIterator();
      for (Observer observer : observers) {
        iterator.addObserver(observer);
      }
      observers.clear();
      return iterator;
    }
  }
  