| /** |
| * 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.storm.streams.operations; |
| |
| /** |
| * Interface for aggregating values. |
| * |
| * @param <T> the original value type |
| * @param <A> the accumulator type |
| * @param <R> the result type |
| */ |
| public interface CombinerAggregator<T, A, R> extends Operation { |
| /** |
| * A static factory to create a {@link CombinerAggregator} based on initial value, accumulator and combiner. |
| * |
| * @param initialValue the initial value of the result to start with |
| * @param accumulator a function that accumulates values into a partial result |
| * @param combiner a function that combines partially accumulated results |
| * @param <T> the value type |
| * @param <R> the result type |
| * @return the {@link CombinerAggregator} |
| */ |
| static <T, R> CombinerAggregator<T, R, R> of(R initialValue, |
| BiFunction<? super R, ? super T, ? extends R> accumulator, |
| BiFunction<? super R, ? super R, ? extends R> combiner) { |
| return new CombinerAggregator<T, R, R>() { |
| @Override |
| public R init() { |
| return initialValue; |
| } |
| |
| @Override |
| public R apply(R aggregate, T value) { |
| return accumulator.apply(aggregate, value); |
| } |
| |
| @Override |
| public R merge(R accum1, R accum2) { |
| return combiner.apply(accum1, accum2); |
| } |
| |
| @Override |
| public R result(R accum) { |
| return accum; |
| } |
| }; |
| } |
| |
| /** |
| * The initial value of the accumulator to start with. |
| * |
| * @return the initial value of the accumulator |
| */ |
| A init(); |
| |
| /** |
| * Updates the accumulator by applying the current accumulator with the value. |
| * |
| * @param accumulator the current accumulator |
| * @param value the value |
| * @return the updated accumulator |
| */ |
| A apply(A accumulator, T value); |
| |
| /** |
| * Merges two accumulators and returns the merged accumulator. |
| * |
| * @param accum1 the first accumulator |
| * @param accum2 the second accumulator |
| * @return the merged accumulator |
| */ |
| A merge(A accum1, A accum2); |
| |
| /** |
| * Produces a result value out of the accumulator. |
| * |
| * @param accum the accumulator |
| * @return the result |
| */ |
| R result(A accum); |
| |
| } |