Add Checkstyle rule to force comments to classes and methods to be Javadoc comments (#4239)

benchmarks/src/main/java/io/druid/benchmark/datagen/EnumeratedTreeDistribution.java

@@ -25,7 +25,7 @@ import org.apache.commons.math3.util.Pair;
 import java.util.List;
 import java.util.TreeMap;
 
-/*
+/**
  * EnumeratedDistrubtion's sample() method does a linear scan through the array of probabilities.
  *
  * This is too slow with high cardinality value sets, so this subclass overrides sample() to use

benchmarks/src/main/java/io/druid/benchmark/datagen/RealRoundingDistribution.java

@@ -22,7 +22,7 @@ package io.druid.benchmark.datagen;
 import org.apache.commons.math3.distribution.AbstractIntegerDistribution;
 import org.apache.commons.math3.distribution.AbstractRealDistribution;
 
-/*
+/**
  * Rounds the output values from the sample() function of an AbstractRealDistribution.
  */
 public class RealRoundingDistribution extends AbstractIntegerDistribution

codestyle/checkstyle.xml

@@ -53,5 +53,10 @@
       <property name="format" value="^// {2}"/>
       <property name="illegalPattern" value="true"/>
     </module>
+    <module name="Regexp">
+      <!-- Force comments to classes and methods to be Javadoc comments -->
+      <property name="format" value="/\*[^\*].*?\n(\s*\*.*?\n)*\s+\*/[\s\n]*(transient|volatile|strictfp|synchronized|native|abstract|class|interface|enum|static|private|public|protected|default|void|byte|char|short|int|float|long|double|[A-Z])"/>
+      <property name="illegalPattern" value="true"/>
+    </module>
   </module>
 </module>

indexing-hadoop/src/main/java/io/druid/indexer/DetermineHashedPartitionsJob.java

@@ -82,7 +82,7 @@ public class DetermineHashedPartitionsJob implements Jobby
        * Group by (timestamp, dimensions) so we can correctly count dimension values as they would appear
        * in the final segment.
        */
-      long startTime = System.currentTimeMillis();
+      final long startTime = System.currentTimeMillis();
       final Job groupByJob = Job.getInstance(
           new Configuration(),
           String.format("%s-determine_partitions_hashed-%s", config.getDataSource(), config.getIntervals())

integration-tests/src/main/java/org/testng/TestNG.java

@@ -2211,7 +2211,7 @@ public class TestNG
   private URLClassLoader m_serviceLoaderClassLoader;
   private List<ITestNGListener> m_serviceLoaderListeners = Lists.newArrayList();
 
-  /*
+  /**
    * Used to test ServiceClassLoader
    */
   public void setServiceLoaderClassLoader(URLClassLoader ucl)
@@ -2219,7 +2219,7 @@ public class TestNG
     m_serviceLoaderClassLoader = ucl;
   }
 
-  /*
+  /**
    * Used to test ServiceClassLoader
    */
   private void addServiceLoaderListener(ITestNGListener l)
@@ -2227,7 +2227,7 @@ public class TestNG
     m_serviceLoaderListeners.add(l);
   }
 
-  /*
+  /**
    * Used to test ServiceClassLoader
    */
   public List<ITestNGListener> getServiceLoaderListeners()

processing/src/main/java/io/druid/query/aggregation/BufferAggregator.java

@@ -127,7 +127,7 @@ public interface BufferAggregator extends HotLoopCallee
   {
   }
 
-  /*
+  /**
    * Relocates any cached objects.
    * If underlying ByteBuffer used for aggregation buffer relocates to a new ByteBuffer, positional caches(if any)
    * built on top of old ByteBuffer can not be used for further {@link BufferAggregator#aggregate(ByteBuffer, int)}

processing/src/main/java/io/druid/query/groupby/epinephelinae/Groupers.java

@@ -34,7 +34,7 @@ public class Groupers
   private static final int C1 = 0xcc9e2d51;
   private static final int C2 = 0x1b873593;
 
-  /*
+  /**
    * This method was rewritten in Java from an intermediate step of the Murmur hash function in
    * https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp, which contained the
    * following header:

processing/src/main/java/io/druid/query/metadata/metadata/SegmentMetadataQuery.java

@@ -45,7 +45,8 @@ import java.util.Objects;
 
 public class SegmentMetadataQuery extends BaseQuery<SegmentAnalysis>
 {
-  /* The SegmentMetadataQuery cache key may contain UTF-8 column name strings.
+  /**
+   * The SegmentMetadataQuery cache key may contain UTF-8 column name strings.
    * Prepend 0xFF before the analysisTypes as a separator to avoid
    * any potential confusion with string values.
    */

processing/src/main/java/io/druid/segment/data/CompressionFactory.java

@@ -63,7 +63,7 @@ public class CompressionFactory
   // encoding format for segments created prior to the introduction of encoding formats
   public static final LongEncodingFormat LEGACY_LONG_ENCODING_FORMAT = LongEncodingFormat.LONGS;
 
-  /*
+  /**
    * Delta Encoding Header v1:
    * Byte 1 : version
    * Byte 2 - 9 : base value
@@ -71,7 +71,7 @@ public class CompressionFactory
    */
   public static final byte DELTA_ENCODING_VERSION = 0x1;
 
-  /*
+  /**
    * Table Encoding Header v1 :
    * Byte 1 : version
    * Byte 2 - 5 : table size
@@ -112,7 +112,7 @@ public class CompressionFactory
     return hasEncodingFlag(strategyId) ? (byte) (strategyId + FLAG_VALUE) : strategyId;
   }
 
-  /*
+  /**
    * The compression of decompression of encodings are separated into different enums. EncodingStrategy refers to the
    * strategy used to encode the data, and EncodingFormat refers to the format the data is encoded in. Note there is not
    * necessarily an one-to-one mapping between to two. For instance, the AUTO LongEncodingStrategy scans the data once
@@ -120,7 +120,6 @@ public class CompressionFactory
    * write in any of the LongEncodingFormat. On the other hand, there are no LongEncodingStrategy that always write in
    * TABLE LongEncodingFormat since it only works for data with low cardinality.
    */
-
   public enum LongEncodingStrategy
   {
     /**

processing/src/main/java/io/druid/segment/incremental/IncrementalIndex.java

@@ -595,7 +595,7 @@ public abstract class IncrementalIndex<AggregatorType> implements Iterable<Row>,
     return capabilities;
   }
 
-  /*
+  /**
    * Currently called to initialize IncrementalIndex dimension order during index creation
    * Index dimension ordering could be changed to initialize from DimensionsSpec after resolution of
    * https://github.com/druid-io/druid/issues/2011