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.apache.beam.sdk.transforms.GroupByKey;
  import org.apache.beam.sdk.transforms.windowing.Trigger.OnceTrigger;
  import org.joda.time.Instant;
  
  /**
   * A {@link Trigger} which never fires.
   *
   * <p>Using this trigger will only produce output when the watermark passes the end of the {@link
   * BoundedWindow window} plus the {@link Window#withAllowedLateness allowed lateness}.
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public final class Never {
    /**
     * Returns a trigger which never fires. Output will be produced from the using {@link GroupByKey}
     * when the {@link BoundedWindow} closes.
     */
    public static NeverTrigger ever() {
      // NeverTrigger ignores all inputs and is Window-type independent.
      return new NeverTrigger();
    }
  
    /** The actual trigger class for {@link Never} triggers. */
    public static class NeverTrigger extends OnceTrigger {
      private NeverTrigger() {
        super(null);
      }
  
      @Override
      protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
        return this;
      }
  
      @Override
      public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
        return BoundedWindow.TIMESTAMP_MAX_VALUE;
      }
    }
  }
  