Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/729#discussion_r102874862
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/statistics/MergedStatisticFactory.java
---
@@ -0,0 +1,46 @@
+/*
+ * 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
+ * <p/>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p/>
+ * 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.drill.exec.physical.impl.statistics;
+
+public class MergedStatisticFactory {
+ /*
+ * Creates the appropriate statistics object given the name of the
statistics and the input statistic
+ */
+ public static MergedStatistic getMergedStatistic(String outputStatName,
String inputStatName) {
+ if (outputStatName == null || inputStatName == null) {
+ return null;
+ } else if (outputStatName.equals(Statistic.COLNAME)) {
+ return new ColumnMergedStatistic(outputStatName, inputStatName);
+ } else if (outputStatName.equals(Statistic.COLTYPE)) {
+ return new ColTypeMergedStatistic(outputStatName, inputStatName);
+ } else if (outputStatName.equals(Statistic.STATCOUNT)) {
+ return new StatCountMergedStatistic(outputStatName, inputStatName);
+ } else if (outputStatName.equals(Statistic.NNSTATCOUNT)) {
+ return new NNStatCountMergedStatistic(outputStatName, inputStatName);
+ } else if (outputStatName.equals(Statistic.AVG_WIDTH)) {
+ return new AvgWidthMergedStatistic(outputStatName, inputStatName);
+ } else if (outputStatName.equals(Statistic.HLL_MERGE)) {
+ return new HLLMergedStatistic(outputStatName, inputStatName);
+ } else if (outputStatName.equals(Statistic.NDV)) {
+ return new NDVMergedStatistic(outputStatName, inputStatName);
--- End diff --
Consider:
```
if (outputStatName.equals(Statistic.NDV)) {
stat = new NDVMergedStatistic();
}
...
stat.init(outputStatName, inputStatName);
```
How often will this factory be used? If frequently, then consider:
```
class Factory() {
private Factory instance = new Factory();
private HashMap<String,Class<? extends MergedStatistic>> statsClasses =
new HashMap<>( );
private Factory() {
statsClasses.put(Statistic.NDV, NDVMergedStatistic.class);
...
}
public MergedStatistic getMergedStatistic(String outputStatName, String
inputStatName) {
return instance.newMergedStatistic(outputStatName, inputStatName);
}
private MergedStatistic instance.newMergedStatistic(String
outputStatName, String inputStatName) {
MergedStatistic stat = statsClasses.get(outputStatName).newInstance();
stat.init(outputStatName, inputStatName);
return stat;
}
```
Lots of ways to do the above; this is just an example.
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