/*
* 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.flink.api.java.summarize.aggregation;
import java.lang.reflect.ParameterizedType;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
/**
* This harness uses multiple aggregators and variously aggregates and combines against
* a list of values while calling a compareResults() method.
*
* This method breaks the rule of "testing only one thing" by aggregating and combining
* a bunch of different ways but can help uncover various kinds of bugs that can show
* up in aggregators.
*
* @param <T> the type to aggregate
* @param <R> the type of the results of the aggregation
* @param <A> the aggregator to use
*/
public abstract class AggregateCombineHarness<T,R,A extends Aggregator<T,R>> {
/**
* Compare results from different runs of aggregate/combine to make sure they are the same.
*
* Subclasses should cause an Assertion failure or throw an Exception if the results aren't
* equal or at least close enough.
*/
protected abstract void compareResults(R result1, R result2);
/**
* Variously aggregate and combine against a list of values, comparing results each time.
*/
@SafeVarargs
public final R summarize(T... values) {
if (values.length == 0 ) {
// when there is nothing to aggregate just combine two empty aggregators and get the result.
A agg1 = initAggregator();
agg1.combine(initAggregator());
return agg1.result();
}
else {
R previousResult = null;
R result = null;
// Shuffling the values might cause test instability but only in the
// case that there are underlying bugs that need to be fixed
List<T> list = Arrays.asList(values);
Collections.shuffle(list);
for (int i = 0; i < values.length; i++ ) {
// Two aggregators are used so that combine() can be tested also.
// It shouldn't matter which aggregator is used because they are combined at the end so
// we're looping through all points of the data and making sure it doesn't make a difference.
A aggregator1 = initAggregator();
A aggregator2 = initAggregator();
for (int j = 0; j < i; j++) {
aggregator1.aggregate(list.get(j));
}
for (int j = i; j < values.length; j++){
aggregator2.aggregate(list.get(j));
}
aggregator1.combine(aggregator2);
previousResult = result;
result = aggregator1.result();
if (previousResult != null) {
// validate that variously aggregating then combining doesn't give different results
compareResults(result, previousResult);
}
}
return result;
}
}
@SuppressWarnings("unchecked")
private A initAggregator() {
try {
// Instantiate a generic type
// http://stackoverflow.com/questions/75175/create-instance-of-generic-type-in-java
return (A) ((Class)((ParameterizedType)this.getClass().getGenericSuperclass()).getActualTypeArguments()[2]).newInstance();
}
catch (Exception e) {
throw new RuntimeException("Could not initialize aggregator", e);
}
}
}