heron/api/src/java/com/twitter/heron/api/windowing/TimestampExtractor.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;

import java.io.Serializable;

import com.twitter.heron.api.tuple.Tuple;

/**
 * Interface to be implemented for extracting timestamp from a tuple.
 */
public interface TimestampExtractor extends Serializable {
  /**
   * Return the tuple timestamp indicating the time when the event happened.
   *
   * @param tuple the tuple
   * @return the timestamp
   */
  long extractTimestamp(Tuple tuple);
}