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.transforms.windowing;
  
  import java.util.List;
  import org.joda.time.Instant;
  
  /**
   * A trigger that is equivalent to {@code Repeatedly.forever(AfterWatermark.pastEndOfWindow())}. See
   * {@link Repeatedly#forever} and {@link AfterWatermark#pastEndOfWindow} for more details.
   *
   * <p>This is a distinguished class to make it easy for runners to optimize for this common case.
   */
  public class DefaultTrigger extends Trigger {
  
    private DefaultTrigger() {
      super();
    }
  
    /** Returns the default trigger. */
    public static DefaultTrigger of() {
      return new DefaultTrigger();
    }
  
    @Override
    public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
      return window.maxTimestamp();
    }
  
    /** @return false; the default trigger never finishes */
    @Override
    public boolean mayFinish() {
      return false;
    }
  
    @Override
    public boolean isCompatible(Trigger other) {
      // Semantically, all default triggers are identical
      return other instanceof DefaultTrigger;
    }
  
    @Override
    protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
      return this;
    }
  }
  