heron/api/src/java/com/twitter/heron/api/windowing/Event.java

//  Copyright 2017 Twitter. All rights reserved.
//
//  Licensed 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 com.twitter.heron.api.windowing;

/**
 * An event is a wrapper object that gets stored in the window.
 *
 * @param <T> the type of the object thats wrapped. E.g Tuple
 */
public interface Event<T> {
  /**
   * The event timestamp in millis. This could be the time
   * when the source generated the tuple or the time
   * when the tuple was received by a bolt.
   *
   * @return the event timestamp in milliseconds.
   */
  long getTimestamp();

  /**
   * Returns the wrapped object, E.g. a tuple
   *
   * @return the wrapped object.
   */
  T get();

  /**
   * If this is a watermark event or not. Watermark events are used
   * for tracking time while processing event based ts.
   *
   * @return true if this is a watermark event
   */
  boolean isWatermark();
}