heron/api/src/java/com/twitter/heron/api/metric/ICombiner.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;

/**
 * Interface for classes that are able to combine multiple objects into one result.
 * @param <T> the type of the input values and the combined value.
 */
public interface ICombiner<T> {
  T identity();

  T combine(T a, T b);
}