IReducer.java

// Copyright 2016 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.metric;

/**
 * Apply an update to an accumulator for which a result can be extracted.
 * @param <T> accumulator to hold and update state
 * @param <U> type of input that can be handled
 * @param <V> type of reduced value from the accumulator
 */
public interface IReducer<T, U, V> {
  T init();

  T reduce(T accumulator, U input);

  V extractResult(T accumulator);
}