Spotbugs: NP_STORE_INTO_NONNULL_FIELD (#8021)

codestyle/spotbugs-exclude.xml

@@ -70,7 +70,6 @@
     <Bug pattern="NP_NULL_PARAM_DEREF"/>
     <Bug pattern="NP_NULL_PARAM_DEREF_NONVIRTUAL"/>
     <Bug pattern="NP_PARAMETER_MUST_BE_NONNULL_BUT_MARKED_AS_NULLABLE"/>
-    <Bug pattern="NP_STORE_INTO_NONNULL_FIELD"/>
     <Bug pattern="NS_DANGEROUS_NON_SHORT_CIRCUIT"/>
     <Bug pattern="OBL_UNSATISFIED_OBLIGATION"/>
     <Bug pattern="OS_OPEN_STREAM"/>

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildAggregator.java

@@ -24,11 +24,14 @@ import com.yahoo.sketches.quantiles.UpdateDoublesSketch;
 import org.apache.druid.query.aggregation.Aggregator;
 import org.apache.druid.segment.ColumnValueSelector;
 
+import javax.annotation.Nullable;
+
 public class DoublesSketchBuildAggregator implements Aggregator
 {
 
   private final ColumnValueSelector<Double> valueSelector;
 
+  @Nullable
   private UpdateDoublesSketch sketch;
 
   public DoublesSketchBuildAggregator(final ColumnValueSelector<Double> valueSelector, final int size)

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchMergeAggregator.java

@@ -24,10 +24,13 @@ import com.yahoo.sketches.quantiles.DoublesUnion;
 import org.apache.druid.query.aggregation.Aggregator;
 import org.apache.druid.segment.ColumnValueSelector;
 
+import javax.annotation.Nullable;
+
 public class DoublesSketchMergeAggregator implements Aggregator
 {
 
   private final ColumnValueSelector selector;
+  @Nullable
   private DoublesUnion union;
 
   public DoublesSketchMergeAggregator(final ColumnValueSelector selector, final int k)

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchAggregator.java

@@ -26,12 +26,16 @@ import org.apache.druid.java.util.common.ISE;
 import org.apache.druid.query.aggregation.Aggregator;
 import org.apache.druid.segment.BaseObjectColumnValueSelector;
 
+import javax.annotation.Nullable;
+
 import java.util.List;
 
 public class SketchAggregator implements Aggregator
 {
   private final BaseObjectColumnValueSelector selector;
   private final int size;
+
+  @Nullable
   private Union union;
 
   public SketchAggregator(BaseObjectColumnValueSelector selector, int size)

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchHolder.java

@@ -35,6 +35,8 @@ import org.apache.druid.java.util.common.IAE;
 import org.apache.druid.java.util.common.ISE;
 import org.apache.druid.java.util.common.StringUtils;
 
+import javax.annotation.Nullable;
+
 import java.util.Arrays;
 import java.util.Comparator;
 
@@ -49,7 +51,7 @@ public class SketchHolder
   );
 
   public static final Comparator<Object> COMPARATOR = Ordering.from(
-      new Comparator()
+      new Comparator<Object>()
       {
         @Override
         public int compare(Object o1, Object o2)
@@ -108,7 +110,9 @@ public class SketchHolder
 
   private final Object obj;
 
+  @Nullable
   private volatile Double cachedEstimate = null;
+  @Nullable
   private volatile Sketch cachedSketch = null;
 
   private SketchHolder(Object obj)

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchBuildAggregator.java

@@ -26,6 +26,8 @@ import org.apache.druid.segment.BaseDoubleColumnValueSelector;
 import org.apache.druid.segment.DimensionSelector;
 import org.apache.druid.segment.data.IndexedInts;
 
+import javax.annotation.Nullable;
+
 import java.util.List;
 
 /**
@@ -38,7 +40,9 @@ public class ArrayOfDoublesSketchBuildAggregator implements Aggregator
 
   private final DimensionSelector keySelector;
   private final BaseDoubleColumnValueSelector[] valueSelectors;
+  @Nullable
   private double[] values; // not part of the state, but to reuse in aggregate() method
+  @Nullable
   private ArrayOfDoublesUpdatableSketch sketch;
 
   public ArrayOfDoublesSketchBuildAggregator(

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchBuildBufferAggregator.java

@@ -30,6 +30,8 @@ import org.apache.druid.segment.BaseDoubleColumnValueSelector;
 import org.apache.druid.segment.DimensionSelector;
 import org.apache.druid.segment.data.IndexedInts;
 
+import javax.annotation.Nullable;
+
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.util.List;
@@ -50,6 +52,7 @@ public class ArrayOfDoublesSketchBuildBufferAggregator implements BufferAggregat
   private final BaseDoubleColumnValueSelector[] valueSelectors;
   private final int nominalEntries;
   private final int maxIntermediateSize;
+  @Nullable
   private double[] values; // not part of the state, but to reuse in aggregate() method
   private final Striped<ReadWriteLock> stripedLock = Striped.readWriteLock(NUM_STRIPES);
 

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchMergeAggregator.java

@@ -25,6 +25,8 @@ import com.yahoo.sketches.tuple.ArrayOfDoublesUnion;
 import org.apache.druid.query.aggregation.Aggregator;
 import org.apache.druid.segment.BaseObjectColumnValueSelector;
 
+import javax.annotation.Nullable;
+
 /**
  * This aggregator merges existing sketches.
  * The input column contains ArrayOfDoublesSketch.
@@ -34,6 +36,7 @@ public class ArrayOfDoublesSketchMergeAggregator implements Aggregator
 {
 
   private final BaseObjectColumnValueSelector<ArrayOfDoublesSketch> selector;
+  @Nullable
   private ArrayOfDoublesUnion union;
 
   public ArrayOfDoublesSketchMergeAggregator(

processing/src/main/java/org/apache/druid/query/groupby/GroupByQueryEngine.java

@@ -298,14 +298,13 @@ public class GroupByQueryEngine
     private final ByteBuffer metricsBuffer;
     private final int maxIntermediateRows;
 
-    private final List<DimensionSpec> dimensionSpecs;
     private final List<DimensionSelector> dimensions;
     private final ArrayList<String> dimNames;
-    private final List<AggregatorFactory> aggregatorSpecs;
     private final BufferAggregator[] aggregators;
     private final String[] metricNames;
     private final int[] sizesRequired;
 
+    @Nullable
     private List<ByteBuffer> unprocessedKeys;
     private Iterator<Row> delegate;
 
@@ -320,7 +319,7 @@ public class GroupByQueryEngine
 
       unprocessedKeys = null;
       delegate = Collections.emptyIterator();
-      dimensionSpecs = query.getDimensions();
+      List<DimensionSpec> dimensionSpecs = query.getDimensions();
       dimensions = Lists.newArrayListWithExpectedSize(dimensionSpecs.size());
       dimNames = Lists.newArrayListWithExpectedSize(dimensionSpecs.size());
 
@@ -340,7 +339,7 @@ public class GroupByQueryEngine
         dimNames.add(dimSpec.getOutputName());
       }
 
-      aggregatorSpecs = query.getAggregatorSpecs();
+      List<AggregatorFactory> aggregatorSpecs = query.getAggregatorSpecs();
       aggregators = new BufferAggregator[aggregatorSpecs.size()];
       metricNames = new String[aggregatorSpecs.size()];
       sizesRequired = new int[aggregatorSpecs.size()];

processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferArrayGrouper.java

@@ -28,6 +28,8 @@ import org.apache.druid.query.aggregation.AggregatorAdapters;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.groupby.epinephelinae.column.GroupByColumnSelectorStrategy;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
@@ -59,7 +61,9 @@ public class BufferArrayGrouper implements VectorGrouper, IntGrouper
   private ByteBuffer valBuffer;
 
   // Scratch objects used by aggregateVector(). Only set if initVectorized() is called.
+  @Nullable
   private int[] vAggregationPositions = null;
+  @Nullable
   private int[] vAggregationRows = null;
 
   static long requiredBufferCapacity(

processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/BufferHashGrouper.java

@@ -28,10 +28,11 @@ import org.apache.druid.java.util.common.parsers.CloseableIterator;
 import org.apache.druid.query.aggregation.AggregatorAdapters;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 
+import javax.annotation.Nullable;
+
 import java.nio.ByteBuffer;
 import java.util.AbstractList;
 import java.util.Collections;
-import java.util.Comparator;
 import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.function.ToIntFunction;
@@ -42,7 +43,6 @@ public class BufferHashGrouper<KeyType> extends AbstractBufferHashGrouper<KeyTyp
   private static final int DEFAULT_INITIAL_BUCKETS = 1024;
   private static final float DEFAULT_MAX_LOAD_FACTOR = 0.7f;
 
-  private ByteBuffer buffer;
   private boolean initialized = false;
 
   // The BufferHashGrouper normally sorts by all fields of the grouping key with lexicographic ascending order.
@@ -54,16 +54,17 @@ public class BufferHashGrouper<KeyType> extends AbstractBufferHashGrouper<KeyTyp
   // to get a comparator that uses the ordering defined by the OrderByColumnSpec of a query.
   private final boolean useDefaultSorting;
 
-  // Track the offsets of used buckets using this list.
+  @Nullable
-  // When a new bucket is initialized by initializeNewBucketKey(), an offset is added to this list.
-  // When expanding the table, the list is reset() and filled with the new offsets of the copied buckets.
-  private ByteBuffer offsetListBuffer;
   private ByteBufferIntList offsetList;
 
   // Scratch objects used by aggregateVector(). Only set if initVectorized() is called.
+  @Nullable
   private ByteBuffer vKeyBuffer = null;
+  @Nullable
   private int[] vKeyHashCodes = null;
+  @Nullable
   private int[] vAggregationPositions = null;
+  @Nullable
   private int[] vAggregationRows = null;
 
   public BufferHashGrouper(
@@ -93,7 +94,7 @@ public class BufferHashGrouper<KeyType> extends AbstractBufferHashGrouper<KeyTyp
   public void init()
   {
     if (!initialized) {
-      this.buffer = bufferSupplier.get();
+      ByteBuffer buffer = bufferSupplier.get();
 
       int hashTableSize = ByteBufferHashTable.calculateTableArenaSizeWithPerBucketAdditionalSize(
           buffer.capacity(),
@@ -106,7 +107,10 @@ public class BufferHashGrouper<KeyType> extends AbstractBufferHashGrouper<KeyTyp
       hashTableBuffer.limit(hashTableSize);
       hashTableBuffer = hashTableBuffer.slice();
 
-      offsetListBuffer = buffer.duplicate();
+      // Track the offsets of used buckets using this list.
+      // When a new bucket is initialized by initializeNewBucketKey(), an offset is added to this list.
+      // When expanding the table, the list is reset() and filled with the new offsets of the copied buckets.
+      ByteBuffer offsetListBuffer = buffer.duplicate();
       offsetListBuffer.position(hashTableSize);
       offsetListBuffer.limit(buffer.capacity());
       offsetListBuffer = offsetListBuffer.slice();
@@ -315,11 +319,7 @@ public class BufferHashGrouper<KeyType> extends AbstractBufferHashGrouper<KeyTyp
       // Sort offsets in-place.
       Collections.sort(
           wrappedOffsets,
-          new Comparator<Integer>()
+          (lhs, rhs) -> {
-          {
-            @Override
-            public int compare(Integer lhs, Integer rhs)
-            {
             final ByteBuffer tableBuffer = hashTable.getTableBuffer();
             return comparator.compare(
                 tableBuffer,
@@ -328,7 +328,6 @@ public class BufferHashGrouper<KeyType> extends AbstractBufferHashGrouper<KeyTyp
                 rhs + HASH_SIZE
             );
           }
-          }
       );
 
       return new CloseableIterator<Entry<KeyType>>()

processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/GroupByQueryEngineV2.java

@@ -363,6 +363,7 @@ public class GroupByQueryEngineV2
     protected final GroupByColumnSelectorPlus[] dims;
     protected final DateTime timestamp;
 
+    @Nullable
     protected CloseableGrouperIterator<KeyType, Row> delegate = null;
     protected final boolean allSingleValueDims;
 

processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/RowBasedGrouperHelper.java

@@ -256,14 +256,7 @@ public class RowBasedGrouperHelper
         valueTypes
     );
 
-    final Accumulator<AggregateResult, Row> accumulator = new Accumulator<AggregateResult, Row>()
+    final Accumulator<AggregateResult, Row> accumulator = (priorResult, row) -> {
-    {
-      @Override
-      public AggregateResult accumulate(
-          final AggregateResult priorResult,
-          final Row row
-      )
-      {
       BaseQuery.checkInterrupted();
 
       if (priorResult != null && !priorResult.isOk()) {
@@ -284,7 +277,6 @@ public class RowBasedGrouperHelper
       columnSelectorRow.set(null);
 
       return aggregateResult;
-      }
     };
 
     return new Pair<>(grouper, accumulator);
@@ -302,33 +294,12 @@ public class RowBasedGrouperHelper
   {
     if (isInputRaw) {
       if (query.getGranularity() instanceof AllGranularity) {
-        return new TimestampExtractFunction()
+        return row -> query.getIntervals().get(0).getStartMillis();
-        {
-          @Override
-          public long apply(Row row)
-          {
-            return query.getIntervals().get(0).getStartMillis();
-          }
-        };
       } else {
-        return new TimestampExtractFunction()
+        return row -> query.getGranularity().bucketStart(row.getTimestamp()).getMillis();
-        {
-          @Override
-          public long apply(Row row)
-          {
-            return query.getGranularity().bucketStart(row.getTimestamp()).getMillis();
-          }
-        };
       }
     } else {
-      return new TimestampExtractFunction()
+      return Row::getTimestampFromEpoch;
-      {
-        @Override
-        public long apply(Row row)
-        {
-          return row.getTimestampFromEpoch();
-        }
-      };
     }
   }
 
@@ -358,60 +329,40 @@ public class RowBasedGrouperHelper
       );
 
       if (includeTimestamp) {
-        return new ValueExtractFunction()
+        return (row, key) -> {
-        {
-          @Override
-          public Comparable[] apply(Row row, Comparable[] key)
-          {
           key[0] = timestampExtractFn.apply(row);
           for (int i = 1; i < key.length; i++) {
             final Comparable val = inputRawSuppliers[i - 1].get();
             key[i] = valueConvertFns[i - 1].apply(val);
           }
           return key;
-          }
         };
       } else {
-        return new ValueExtractFunction()
+        return (row, key) -> {
-        {
-          @Override
-          public Comparable[] apply(Row row, Comparable[] key)
-          {
           for (int i = 0; i < key.length; i++) {
             final Comparable val = inputRawSuppliers[i].get();
             key[i] = valueConvertFns[i].apply(val);
           }
           return key;
-          }
         };
       }
     } else {
       if (includeTimestamp) {
-        return new ValueExtractFunction()
+        return (row, key) -> {
-        {
-          @Override
-          public Comparable[] apply(Row row, Comparable[] key)
-          {
           key[0] = timestampExtractFn.apply(row);
           for (int i = 1; i < key.length; i++) {
             final Comparable val = (Comparable) row.getRaw(query.getDimensions().get(i - 1).getOutputName());
             key[i] = valueConvertFns[i - 1].apply(val);
           }
           return key;
-          }
         };
       } else {
-        return new ValueExtractFunction()
+        return (row, key) -> {
-        {
-          @Override
-          public Comparable[] apply(Row row, Comparable[] key)
-          {
           for (int i = 0; i < key.length; i++) {
             final Comparable val = (Comparable) row.getRaw(query.getDimensions().get(i).getOutputName());
             key[i] = valueConvertFns[i].apply(val);
           }
           return key;
-          }
         };
       }
     }
@@ -437,11 +388,7 @@ public class RowBasedGrouperHelper
 
     return new CloseableGrouperIterator<>(
         grouper.iterator(true),
-        new Function<Grouper.Entry<RowBasedKey>, Row>()
+        entry -> {
-        {
-          @Override
-          public Row apply(Grouper.Entry<RowBasedKey> entry)
-          {
           Map<String, Object> theMap = Maps.newLinkedHashMap();
 
           // Get timestamp, maybe.
@@ -486,7 +433,6 @@ public class RowBasedGrouperHelper
           }
 
           return new MapBasedRow(timestamp, theMap);
-          }
         },
         closeable
     );
@@ -713,25 +659,16 @@ public class RowBasedGrouperHelper
 
       if (includeTimestamp) {
         if (sortByDimsFirst) {
-          return new Comparator<Grouper.Entry<RowBasedKey>>()
+          return (entry1, entry2) -> {
-          {
-            @Override
-            public int compare(Grouper.Entry<RowBasedKey> entry1, Grouper.Entry<RowBasedKey> entry2)
-            {
             final int cmp = compareDimsInRows(entry1.getKey(), entry2.getKey(), 1);
             if (cmp != 0) {
               return cmp;
             }
 
             return Longs.compare((long) entry1.getKey().getKey()[0], (long) entry2.getKey().getKey()[0]);
-            }
           };
         } else {
-          return new Comparator<Grouper.Entry<RowBasedKey>>()
+          return (entry1, entry2) -> {
-          {
-            @Override
-            public int compare(Grouper.Entry<RowBasedKey> entry1, Grouper.Entry<RowBasedKey> entry2)
-            {
             final int timeCompare = Longs.compare(
                 (long) entry1.getKey().getKey()[0],
                 (long) entry2.getKey().getKey()[0]
@@ -742,18 +679,10 @@ public class RowBasedGrouperHelper
             }
 
             return compareDimsInRows(entry1.getKey(), entry2.getKey(), 1);
-            }
           };
         }
       } else {
-        return new Comparator<Grouper.Entry<RowBasedKey>>()
+        return (entry1, entry2) -> compareDimsInRows(entry1.getKey(), entry2.getKey(), 0);
-        {
-          @Override
-          public int compare(Grouper.Entry<RowBasedKey> entry1, Grouper.Entry<RowBasedKey> entry2)
-          {
-            return compareDimsInRows(entry1.getKey(), entry2.getKey(), 0);
-          }
-        };
       }
     }
 
@@ -804,11 +733,7 @@ public class RowBasedGrouperHelper
 
       if (includeTimestamp) {
         if (sortByDimsFirst) {
-          return new Comparator<Grouper.Entry<RowBasedKey>>()
+          return (entry1, entry2) -> {
-          {
-            @Override
-            public int compare(Grouper.Entry<RowBasedKey> entry1, Grouper.Entry<RowBasedKey> entry2)
-            {
             final int cmp = compareDimsInRowsWithAggs(
                 entry1,
                 entry2,
@@ -824,14 +749,9 @@ public class RowBasedGrouperHelper
             }
 
             return Longs.compare((long) entry1.getKey().getKey()[0], (long) entry2.getKey().getKey()[0]);
-            }
           };
         } else {
-          return new Comparator<Grouper.Entry<RowBasedKey>>()
+          return (entry1, entry2) -> {
-          {
-            @Override
-            public int compare(Grouper.Entry<RowBasedKey> entry1, Grouper.Entry<RowBasedKey> entry2)
-            {
             final int timeCompare = Longs.compare(
                 (long) entry1.getKey().getKey()[0],
                 (long) entry2.getKey().getKey()[0]
@@ -851,16 +771,10 @@ public class RowBasedGrouperHelper
                 isNumericField,
                 comparators
             );
-            }
           };
         }
       } else {
-        return new Comparator<Grouper.Entry<RowBasedKey>>()
+        return (entry1, entry2) -> compareDimsInRowsWithAggs(
-        {
-          @Override
-          public int compare(Grouper.Entry<RowBasedKey> entry1, Grouper.Entry<RowBasedKey> entry2)
-          {
-            return compareDimsInRowsWithAggs(
             entry1,
             entry2,
             0,
@@ -871,8 +785,6 @@ public class RowBasedGrouperHelper
             comparators
         );
       }
-        };
-      }
     }
 
     private static int compareDimsInRows(RowBasedKey key1, RowBasedKey key2, int dimStart)
@@ -981,6 +893,7 @@ public class RowBasedGrouperHelper
     // dictionary id -> rank of the sorted dictionary
     // This is initialized in the constructor and bufferComparator() with static dictionary and dynamic dictionary,
     // respectively.
+    @Nullable
     private int[] rankOfDictionaryIds = null;
 
     RowBasedKeySerde(
@@ -1118,11 +1031,7 @@ public class RowBasedGrouperHelper
 
       if (includeTimestamp) {
         if (sortByDimsFirst) {
-          return new Grouper.BufferComparator()
+          return (lhsBuffer, rhsBuffer, lhsPosition, rhsPosition) -> {
-          {
-            @Override
-            public int compare(ByteBuffer lhsBuffer, ByteBuffer rhsBuffer, int lhsPosition, int rhsPosition)
-            {
             final int cmp = compareDimsInBuffersForNullFudgeTimestamp(
                 serdeHelperComparators,
                 lhsBuffer,
@@ -1135,14 +1044,9 @@ public class RowBasedGrouperHelper
             }
 
             return Longs.compare(lhsBuffer.getLong(lhsPosition), rhsBuffer.getLong(rhsPosition));
-            }
           };
         } else {
-          return new Grouper.BufferComparator()
+          return (lhsBuffer, rhsBuffer, lhsPosition, rhsPosition) -> {
-          {
-            @Override
-            public int compare(ByteBuffer lhsBuffer, ByteBuffer rhsBuffer, int lhsPosition, int rhsPosition)
-            {
             final int timeCompare = Longs.compare(lhsBuffer.getLong(lhsPosition), rhsBuffer.getLong(rhsPosition));
 
             if (timeCompare != 0) {
@@ -1156,15 +1060,10 @@ public class RowBasedGrouperHelper
                 lhsPosition,
                 rhsPosition
             );
-            }
           };
         }
       } else {
-        return new Grouper.BufferComparator()
+        return (lhsBuffer, rhsBuffer, lhsPosition, rhsPosition) -> {
-        {
-          @Override
-          public int compare(ByteBuffer lhsBuffer, ByteBuffer rhsBuffer, int lhsPosition, int rhsPosition)
-          {
           for (int i = 0; i < dimCount; i++) {
             final int cmp = serdeHelperComparators[i].compare(
                 lhsBuffer,
@@ -1179,7 +1078,6 @@ public class RowBasedGrouperHelper
           }
 
           return 0;
-          }
         };
       }
     }
@@ -1246,11 +1144,7 @@ public class RowBasedGrouperHelper
 
       if (includeTimestamp) {
         if (sortByDimsFirst) {
-          return new Grouper.BufferComparator()
+          return (lhsBuffer, rhsBuffer, lhsPosition, rhsPosition) -> {
-          {
-            @Override
-            public int compare(ByteBuffer lhsBuffer, ByteBuffer rhsBuffer, int lhsPosition, int rhsPosition)
-            {
             final int cmp = compareDimsInBuffersForNullFudgeTimestampForPushDown(
                 adjustedSerdeHelperComparators,
                 needsReverses,
@@ -1265,14 +1159,9 @@ public class RowBasedGrouperHelper
             }
 
             return Longs.compare(lhsBuffer.getLong(lhsPosition), rhsBuffer.getLong(rhsPosition));
-            }
           };
         } else {
-          return new Grouper.BufferComparator()
+          return (lhsBuffer, rhsBuffer, lhsPosition, rhsPosition) -> {
-          {
-            @Override
-            public int compare(ByteBuffer lhsBuffer, ByteBuffer rhsBuffer, int lhsPosition, int rhsPosition)
-            {
             final int timeCompare = Longs.compare(lhsBuffer.getLong(lhsPosition), rhsBuffer.getLong(rhsPosition));
 
             if (timeCompare != 0) {
@@ -1290,15 +1179,10 @@ public class RowBasedGrouperHelper
             );
 
             return cmp;
-            }
           };
         }
       } else {
-        return new Grouper.BufferComparator()
+        return (lhsBuffer, rhsBuffer, lhsPosition, rhsPosition) -> {
-        {
-          @Override
-          public int compare(ByteBuffer lhsBuffer, ByteBuffer rhsBuffer, int lhsPosition, int rhsPosition)
-          {
           for (int i = 0; i < fieldCount; i++) {
             final int cmp;
             if (needsReverses.get(i)) {
@@ -1323,7 +1207,6 @@ public class RowBasedGrouperHelper
           }
 
           return 0;
-          }
         };
       }
     }

processing/src/main/java/org/apache/druid/segment/MetricHolder.java

@@ -26,6 +26,8 @@ import org.apache.druid.segment.data.GenericIndexed;
 import org.apache.druid.segment.serde.ComplexMetricSerde;
 import org.apache.druid.segment.serde.ComplexMetrics;
 
+import javax.annotation.Nullable;
+
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
@@ -96,7 +98,9 @@ public class MetricHolder
   private final String name;
   private final String typeName;
   private final MetricType type;
+  @Nullable
   CompressedColumnarFloatsSupplier floatType = null;
+  @Nullable
   GenericIndexed<?> complexType = null;
 
   private MetricHolder(

processing/src/main/java/org/apache/druid/segment/SingleScanTimeDimensionSelector.java

@@ -46,10 +46,12 @@ public class SingleScanTimeDimensionSelector implements DimensionSelector
 
   private final List<String> timeValues = new ArrayList<>();
   private final SingleIndexedInt row = new SingleIndexedInt();
-  private String currentValue = null;
   private long currentTimestamp = Long.MIN_VALUE;
   private int index = -1;
 
+  @Nullable
+  private String currentValue = null;
+
   public SingleScanTimeDimensionSelector(
       BaseLongColumnValueSelector selector,
       @Nullable ExtractionFn extractionFn,

processing/src/main/java/org/apache/druid/segment/StringDimensionIndexer.java

@@ -232,9 +232,11 @@ public class StringDimensionIndexer implements DimensionIndexer<Integer, int[],
   private final DimensionDictionary dimLookup;
   private final MultiValueHandling multiValueHandling;
   private final boolean hasBitmapIndexes;
-  private SortedDimensionDictionary sortedLookup;
   private boolean hasMultipleValues = false;
 
+  @Nullable
+  private SortedDimensionDictionary sortedLookup;
+
   public StringDimensionIndexer(MultiValueHandling multiValueHandling, boolean hasBitmapIndexes)
   {
     this.dimLookup = new DimensionDictionary();
@@ -252,7 +254,7 @@ public class StringDimensionIndexer implements DimensionIndexer<Integer, int[],
       final int nullId = dimLookup.getId(null);
       encodedDimensionValues = nullId == ABSENT_VALUE_ID ? new int[]{dimLookup.add(null)} : new int[]{nullId};
     } else if (dimValues instanceof List) {
-      List<Object> dimValuesList = (List) dimValues;
+      List<Object> dimValuesList = (List<Object>) dimValues;
       if (dimValuesList.isEmpty()) {
         dimLookup.add(null);
         encodedDimensionValues = IntArrays.EMPTY_ARRAY;

processing/src/main/java/org/apache/druid/segment/StringDimensionMergerV9.java

@@ -77,27 +77,36 @@ public class StringDimensionMergerV9 implements DimensionMergerV9
   private static final Indexed<String> NULL_STR_DIM_VAL = new ListIndexed<>(Collections.singletonList(null));
   private static final Splitter SPLITTER = Splitter.on(",");
 
-  private ColumnarIntsSerializer encodedValueSerializer;
+  private final String dimensionName;
-
-  private String dimensionName;
-  private GenericIndexedWriter<String> dictionaryWriter;
-  private String firstDictionaryValue;
-  private int dictionarySize;
-  private GenericIndexedWriter<ImmutableBitmap> bitmapWriter;
-  private ByteBufferWriter<ImmutableRTree> spatialWriter;
-  private ArrayList<IntBuffer> dimConversions;
-  private int cardinality = 0;
-  private boolean hasNull = false;
-  private MutableBitmap nullRowsBitmap;
-  private final SegmentWriteOutMedium segmentWriteOutMedium;
-  private int rowCount = 0;
-  private ColumnCapabilities capabilities;
-  private List<IndexableAdapter> adapters;
-  private final IndexSpec indexSpec;
-  private IndexMerger.DictionaryMergeIterator dictionaryMergeIterator;
-
   private final ProgressIndicator progress;
   private final Closer closer;
+  private final IndexSpec indexSpec;
+  private final SegmentWriteOutMedium segmentWriteOutMedium;
+  private final MutableBitmap nullRowsBitmap;
+  private final ColumnCapabilities capabilities;
+
+  private int dictionarySize;
+  private int rowCount = 0;
+  private int cardinality = 0;
+  private boolean hasNull = false;
+
+  @Nullable
+  private GenericIndexedWriter<ImmutableBitmap> bitmapWriter;
+  @Nullable
+  private ByteBufferWriter<ImmutableRTree> spatialWriter;
+  @Nullable
+  private ArrayList<IntBuffer> dimConversions;
+  @Nullable
+  private List<IndexableAdapter> adapters;
+  @Nullable
+  private IndexMerger.DictionaryMergeIterator dictionaryMergeIterator;
+  @Nullable
+  private ColumnarIntsSerializer encodedValueSerializer;
+  @Nullable
+  private GenericIndexedWriter<String> dictionaryWriter;
+  @Nullable
+  private String firstDictionaryValue;
+
 
   public StringDimensionMergerV9(
       String dimensionName,
@@ -537,13 +546,12 @@ public class StringDimensionMergerV9 implements DimensionMergerV9
         .withBitmapIndex(bitmapWriter)
         .withSpatialIndex(spatialWriter)
         .withByteOrder(IndexIO.BYTE_ORDER);
-    final ColumnDescriptor serdeficator = builder
-        .addSerde(partBuilder.build())
-        .build();
 
     //log.info("Completed dimension column[%s] in %,d millis.", dimensionName, System.currentTimeMillis() - dimStartTime);
 
-    return serdeficator;
+    return builder
+        .addSerde(partBuilder.build())
+        .build();
   }
 
   protected interface IndexSeeker

processing/src/main/java/org/apache/druid/segment/column/ColumnBuilder.java

@@ -23,18 +23,25 @@ import com.google.common.base.Preconditions;
 import com.google.common.base.Supplier;
 import org.apache.druid.java.util.common.io.smoosh.SmooshedFileMapper;
 
+import javax.annotation.Nullable;
+
 /**
  */
 public class ColumnBuilder
 {
+  @Nullable
   private ValueType type = null;
   private boolean hasMultipleValues = false;
   private boolean filterable = false;
-
-  private Supplier<? extends BaseColumn> columnSupplier = null;
   private boolean dictionaryEncoded = false;
+
+  @Nullable
+  private Supplier<? extends BaseColumn> columnSupplier = null;
+  @Nullable
   private Supplier<BitmapIndex> bitmapIndex = null;
+  @Nullable
   private Supplier<SpatialIndex> spatialIndex = null;
+  @Nullable
   private SmooshedFileMapper fileMapper = null;
 
   public ColumnBuilder setFileMapper(SmooshedFileMapper fileMapper)

processing/src/main/java/org/apache/druid/segment/column/ColumnCapabilitiesImpl.java

@@ -23,12 +23,16 @@ import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import org.apache.druid.java.util.common.ISE;
 
+import javax.annotation.Nullable;
+
 /**
  *
  */
 public class ColumnCapabilitiesImpl implements ColumnCapabilities
 {
+  @Nullable
   private ValueType type = null;
+
   private boolean dictionaryEncoded = false;
   private boolean runLengthEncoded = false;
   private boolean hasInvertedIndexes = false;

processing/src/main/java/org/apache/druid/segment/column/ColumnDescriptor.java

@@ -28,6 +28,8 @@ import org.apache.druid.java.util.common.io.smoosh.SmooshedFileMapper;
 import org.apache.druid.segment.serde.ColumnPartSerde;
 import org.apache.druid.segment.serde.Serializer;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.channels.WritableByteChannel;
@@ -111,7 +113,9 @@ public class ColumnDescriptor implements Serializer
 
   public static class Builder
   {
+    @Nullable
     private ValueType valueType = null;
+    @Nullable
     private Boolean hasMultipleValues = null;
 
     private final List<ColumnPartSerde> parts = new ArrayList<>();

processing/src/main/java/org/apache/druid/segment/data/BlockLayoutColumnarDoublesSerializer.java

@@ -25,6 +25,8 @@ import org.apache.druid.segment.CompressedPools;
 import org.apache.druid.segment.serde.MetaSerdeHelper;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
@@ -45,6 +47,7 @@ public class BlockLayoutColumnarDoublesSerializer implements ColumnarDoublesSeri
   private final CompressionStrategy compression;
 
   private int numInserted = 0;
+  @Nullable
   private ByteBuffer endBuffer;
 
   BlockLayoutColumnarDoublesSerializer(

processing/src/main/java/org/apache/druid/segment/data/BlockLayoutColumnarFloatsSerializer.java

@@ -25,6 +25,8 @@ import org.apache.druid.segment.CompressedPools;
 import org.apache.druid.segment.serde.MetaSerdeHelper;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
@@ -45,6 +47,7 @@ public class BlockLayoutColumnarFloatsSerializer implements ColumnarFloatsSerial
   private final CompressionStrategy compression;
 
   private int numInserted = 0;
+  @Nullable
   private ByteBuffer endBuffer;
 
   BlockLayoutColumnarFloatsSerializer(

processing/src/main/java/org/apache/druid/segment/data/BlockLayoutColumnarLongsSerializer.java

@@ -24,6 +24,8 @@ import org.apache.druid.segment.CompressedPools;
 import org.apache.druid.segment.serde.MetaSerdeHelper;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
@@ -47,6 +49,7 @@ public class BlockLayoutColumnarLongsSerializer implements ColumnarLongsSerializ
   private int numInserted = 0;
   private int numInsertedForNextFlush;
 
+  @Nullable
   private ByteBuffer endBuffer;
 
   BlockLayoutColumnarLongsSerializer(

processing/src/main/java/org/apache/druid/segment/data/ByteBufferWriter.java

@@ -26,6 +26,8 @@ import org.apache.druid.segment.serde.Serializer;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 import org.apache.druid.segment.writeout.WriteOutBytes;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.channels.WritableByteChannel;
 
@@ -36,7 +38,9 @@ public class ByteBufferWriter<T> implements Serializer
   private final SegmentWriteOutMedium segmentWriteOutMedium;
   private final ObjectStrategy<T> strategy;
 
+  @Nullable
   private WriteOutBytes headerOut = null;
+  @Nullable
   private WriteOutBytes valueOut = null;
 
   public ByteBufferWriter(SegmentWriteOutMedium segmentWriteOutMedium, ObjectStrategy<T> strategy)

processing/src/main/java/org/apache/druid/segment/data/CompressedColumnarIntsSerializer.java

@@ -24,6 +24,8 @@ import org.apache.druid.java.util.common.io.smoosh.FileSmoosher;
 import org.apache.druid.segment.serde.MetaSerdeHelper;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
@@ -45,9 +47,11 @@ public class CompressedColumnarIntsSerializer extends SingleValueColumnarIntsSer
   private final int chunkFactor;
   private final CompressionStrategy compression;
   private final GenericIndexedWriter<ByteBuffer> flattener;
-  private ByteBuffer endBuffer;
   private int numInserted;
 
+  @Nullable
+  private ByteBuffer endBuffer;
+
   CompressedColumnarIntsSerializer(
       final SegmentWriteOutMedium segmentWriteOutMedium,
       final String filenameBase,

processing/src/main/java/org/apache/druid/segment/data/CompressedVSizeColumnarIntsSerializer.java

@@ -25,6 +25,8 @@ import org.apache.druid.segment.IndexIO;
 import org.apache.druid.segment.serde.MetaSerdeHelper;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
@@ -67,10 +69,11 @@ public class CompressedVSizeColumnarIntsSerializer extends SingleValueColumnarIn
   private final CompressionStrategy compression;
   private final GenericIndexedWriter<ByteBuffer> flattener;
   private final ByteBuffer intBuffer;
-
-  private ByteBuffer endBuffer;
   private int numInserted;
 
+  @Nullable
+  private ByteBuffer endBuffer;
+
   CompressedVSizeColumnarIntsSerializer(
       final SegmentWriteOutMedium segmentWriteOutMedium,
       final String filenameBase,

processing/src/main/java/org/apache/druid/segment/data/GenericIndexed.java

@@ -198,6 +198,7 @@ public class GenericIndexed<T> implements CloseableIndexed<T>, Serializer
   private int logBaseTwoOfElementsPerValueFile;
   private int relativeIndexMask;
 
+  @Nullable
   private final ByteBuffer theBuffer;
 
   /**

processing/src/main/java/org/apache/druid/segment/data/GenericIndexedWriter.java

@@ -140,10 +140,13 @@ public class GenericIndexedWriter<T> implements Serializer
   private boolean objectsSorted = true;
   @Nullable
   private T prevObject = null;
+  @Nullable
   private WriteOutBytes headerOut = null;
+  @Nullable
   private WriteOutBytes valuesOut = null;
   private int numWritten = 0;
   private boolean requireMultipleFiles = false;
+  @Nullable
   private LongList headerOutLong;
 
   private final ByteBuffer getOffsetBuffer = ByteBuffer.allocate(Integer.BYTES);

processing/src/main/java/org/apache/druid/segment/data/IntermediateColumnarLongsSerializer.java

@@ -27,6 +27,8 @@ import it.unimi.dsi.fastutil.longs.LongList;
 import org.apache.druid.java.util.common.io.smoosh.FileSmoosher;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteOrder;
 import java.nio.channels.WritableByteChannel;
@@ -42,7 +44,6 @@ public class IntermediateColumnarLongsSerializer implements ColumnarLongsSeriali
   private final String filenameBase;
   private final ByteOrder order;
   private final CompressionStrategy compression;
-  private LongList tempOut = null;
 
   private int numInserted = 0;
 
@@ -52,6 +53,9 @@ public class IntermediateColumnarLongsSerializer implements ColumnarLongsSeriali
   private long maxVal = Long.MIN_VALUE;
   private long minVal = Long.MAX_VALUE;
 
+  @Nullable
+  private LongList tempOut = null;
+  @Nullable
   private ColumnarLongsSerializer delegate;
 
   IntermediateColumnarLongsSerializer(

processing/src/main/java/org/apache/druid/segment/data/LongsLongEncodingWriter.java

@@ -21,6 +21,8 @@ package org.apache.druid.segment.data;
 
 import org.apache.druid.segment.writeout.WriteOutBytes;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
@@ -31,7 +33,9 @@ public class LongsLongEncodingWriter implements CompressionFactory.LongEncodingW
 
   private final ByteBuffer orderBuffer;
   private final ByteOrder order;
+  @Nullable
   private ByteBuffer outBuffer = null;
+  @Nullable
   private OutputStream outStream = null;
 
   public LongsLongEncodingWriter(ByteOrder order)

processing/src/main/java/org/apache/druid/segment/data/VSizeColumnarIntsSerializer.java

@@ -26,6 +26,8 @@ import org.apache.druid.segment.serde.MetaSerdeHelper;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 import org.apache.druid.segment.writeout.WriteOutBytes;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.channels.WritableByteChannel;
@@ -46,9 +48,11 @@ public class VSizeColumnarIntsSerializer extends SingleValueColumnarIntsSerializ
   private final int numBytes;
 
   private final ByteBuffer helperBuffer = ByteBuffer.allocate(Integer.BYTES);
-  private WriteOutBytes valuesOut = null;
   private boolean bufPaddingWritten = false;
 
+  @Nullable
+  private WriteOutBytes valuesOut = null;
+
   public VSizeColumnarIntsSerializer(final SegmentWriteOutMedium segmentWriteOutMedium, final int maxValue)
   {
     this.segmentWriteOutMedium = segmentWriteOutMedium;

processing/src/main/java/org/apache/druid/segment/data/VSizeColumnarMultiIntsSerializer.java

@@ -26,6 +26,8 @@ import org.apache.druid.segment.serde.MetaSerdeHelper;
 import org.apache.druid.segment.writeout.SegmentWriteOutMedium;
 import org.apache.druid.segment.writeout.WriteOutBytes;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.channels.WritableByteChannel;
 
@@ -83,7 +85,9 @@ public class VSizeColumnarMultiIntsSerializer extends ColumnarMultiIntsSerialize
   private final WriteInt writeInt;
 
   private final SegmentWriteOutMedium segmentWriteOutMedium;
+  @Nullable
   private WriteOutBytes headerOut = null;
+  @Nullable
   private WriteOutBytes valuesOut = null;
   private int numWritten = 0;
   private boolean numBytesForMaxWritten = false;

processing/src/main/java/org/apache/druid/segment/data/VSizeLongSerde.java

@@ -21,6 +21,8 @@ package org.apache.druid.segment.data;
 
 import org.apache.druid.java.util.common.IAE;
 
+import javax.annotation.Nullable;
+
 import java.io.Closeable;
 import java.io.IOException;
 import java.io.OutputStream;
@@ -189,6 +191,7 @@ public class VSizeLongSerde
 
   private static final class Size1Ser implements LongSerializer
   {
+    @Nullable
     OutputStream output = null;
     ByteBuffer buffer;
     byte curByte = 0;
@@ -242,6 +245,7 @@ public class VSizeLongSerde
 
   private static final class Size2Ser implements LongSerializer
   {
+    @Nullable
     OutputStream output = null;
     ByteBuffer buffer;
     byte curByte = 0;
@@ -295,8 +299,8 @@ public class VSizeLongSerde
 
   private static final class Mult4Ser implements LongSerializer
   {
-
+    @Nullable
-    OutputStream output = null;
+    OutputStream output;
     ByteBuffer buffer;
     int numBytes;
     byte curByte = 0;
@@ -361,6 +365,7 @@ public class VSizeLongSerde
 
   private static final class Mult8Ser implements LongSerializer
   {
+    @Nullable
     OutputStream output;
     ByteBuffer buffer;
     int numBytes;

processing/src/main/java/org/apache/druid/segment/incremental/IncrementalIndex.java

@@ -330,6 +330,7 @@ public abstract class IncrementalIndex<AggregatorType> extends AbstractIndex imp
 
   public static class Builder
   {
+    @Nullable
     private IncrementalIndexSchema incrementalIndexSchema;
     private boolean deserializeComplexMetrics;
     private boolean reportParseExceptions;
@@ -505,8 +506,8 @@ public abstract class IncrementalIndex<AggregatorType> extends AbstractIndex imp
 
   static class IncrementalIndexRowResult
   {
-    private IncrementalIndexRow incrementalIndexRow;
+    private final IncrementalIndexRow incrementalIndexRow;
-    private List<String> parseExceptionMessages;
+    private final List<String> parseExceptionMessages;
 
     IncrementalIndexRowResult(IncrementalIndexRow incrementalIndexRow, List<String> parseExceptionMessages)
     {
@@ -527,9 +528,9 @@ public abstract class IncrementalIndex<AggregatorType> extends AbstractIndex imp
 
   static class AddToFactsResult
   {
-    private int rowCount;
+    private final int rowCount;
     private final long bytesInMemory;
-    private List<String> parseExceptionMessages;
+    private final List<String> parseExceptionMessages;
 
     public AddToFactsResult(
         int rowCount,
@@ -997,11 +998,7 @@ public abstract class IncrementalIndex<AggregatorType> extends AbstractIndex imp
 
   public Iterable<Row> iterableWithPostAggregations(final List<PostAggregator> postAggs, final boolean descending)
   {
-    return new Iterable<Row>()
+    return () -> {
-    {
-      @Override
-      public Iterator<Row> iterator()
-      {
       final List<DimensionDesc> dimensions = getDimensions();
 
       return Iterators.transform(
@@ -1043,7 +1040,6 @@ public abstract class IncrementalIndex<AggregatorType> extends AbstractIndex imp
             return new MapBasedRow(incrementalIndexRow.getTimestamp(), theVals);
           }
       );
-      }
     };
   }
 

processing/src/main/java/org/apache/druid/segment/incremental/IncrementalIndexAdapter.java

@@ -48,6 +48,7 @@ public class IncrementalIndexAdapter implements IndexableAdapter
   private static class DimensionAccessor
   {
     private final IncrementalIndex.DimensionDesc dimensionDesc;
+    @Nullable
     private final MutableBitmap[] invertedIndexes;
     private final DimensionIndexer indexer;
 

processing/src/main/java/org/apache/druid/segment/incremental/IncrementalIndexRowHolder.java

@@ -22,6 +22,8 @@ package org.apache.druid.segment.incremental;
 import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector;
 import org.apache.druid.segment.LongColumnSelector;
 
+import javax.annotation.Nullable;
+
 /**
  * IncrementalIndexRowHolder is a simple {@link #get}/{@link #set} holder of {@link IncrementalIndexRow}. It is used
  * to implement various machinery around {@link IncrementalIndex}, e. g. {@link
@@ -33,6 +35,7 @@ import org.apache.druid.segment.LongColumnSelector;
  */
 public class IncrementalIndexRowHolder implements LongColumnSelector
 {
+  @Nullable
   private IncrementalIndexRow currEntry = null;
 
   public IncrementalIndexRow get()

processing/src/main/java/org/apache/druid/segment/incremental/OffheapIncrementalIndex.java

@@ -33,6 +33,8 @@ import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.aggregation.BufferAggregator;
 import org.apache.druid.segment.ColumnSelectorFactory;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
@@ -59,14 +61,17 @@ public class OffheapIncrementalIndex extends IncrementalIndex<BufferAggregator>
 
   protected final int maxRowCount;
 
+  @Nullable
   private volatile Map<String, ColumnSelectorFactory> selectors;
 
   //given a ByteBuffer and an offset where all aggregates for a row are stored
   //offset + aggOffsetInBuffer[i] would give position in ByteBuffer where ith aggregate
   //is stored
+  @Nullable
   private volatile int[] aggOffsetInBuffer;
   private volatile int aggsTotalSize;
 
+  @Nullable
   private String outOfRowsReason = null;
 
   OffheapIncrementalIndex(

processing/src/main/java/org/apache/druid/segment/incremental/OnheapIncrementalIndex.java

@@ -60,8 +60,10 @@ public class OnheapIncrementalIndex extends IncrementalIndex<Aggregator>
   private final long maxBytesPerRowForAggregators;
   protected final int maxRowCount;
   protected final long maxBytesInMemory;
-  private volatile Map<String, ColumnSelectorFactory> selectors;
 
+  @Nullable
+  private volatile Map<String, ColumnSelectorFactory> selectors;
+  @Nullable
   private String outOfRowsReason = null;
 
   OnheapIncrementalIndex(

processing/src/main/java/org/apache/druid/segment/serde/ComplexColumnPartSerde.java

@@ -22,16 +22,15 @@ package org.apache.druid.segment.serde;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import org.apache.druid.segment.GenericColumnSerializer;
-import org.apache.druid.segment.column.ColumnBuilder;
-import org.apache.druid.segment.column.ColumnConfig;
 
-import java.nio.ByteBuffer;
+import javax.annotation.Nullable;
 
 /**
  */
 public class ComplexColumnPartSerde implements ColumnPartSerde
 {
   private final String typeName;
+  @Nullable
   private final ComplexMetricSerde serde;
   private final Serializer serializer;
 
@@ -70,21 +69,18 @@ public class ComplexColumnPartSerde implements ColumnPartSerde
   @Override
   public Deserializer getDeserializer()
   {
-    return new Deserializer()
+    return (buffer, builder, columnConfig) -> {
-    {
-      @Override
-      public void read(ByteBuffer buffer, ColumnBuilder builder, ColumnConfig columnConfig)
-      {
       if (serde != null) {
         serde.deserializeColumn(buffer, builder);
       }
-      }
     };
   }
 
   public static class SerializerBuilder
   {
+    @Nullable
     private String typeName = null;
+    @Nullable
     private GenericColumnSerializer delegate = null;
 
     public SerializerBuilder withTypeName(final String typeName)

processing/src/main/java/org/apache/druid/segment/serde/DictionaryEncodedColumnPartSerde.java

@@ -143,13 +143,21 @@ public class DictionaryEncodedColumnPartSerde implements ColumnPartSerde
 
   public static class SerializerBuilder
   {
-    private VERSION version = null;
     private int flags = STARTING_FLAGS;
+
+    @Nullable
+    private VERSION version = null;
+    @Nullable
     private GenericIndexedWriter<String> dictionaryWriter = null;
+    @Nullable
     private ColumnarIntsSerializer valueWriter = null;
+    @Nullable
     private BitmapSerdeFactory bitmapSerdeFactory = null;
+    @Nullable
     private GenericIndexedWriter<ImmutableBitmap> bitmapIndexWriter = null;
+    @Nullable
     private ByteBufferWriter<ImmutableRTree> spatialIndexWriter = null;
+    @Nullable
     private ByteOrder byteOrder = null;
 
     public SerializerBuilder withDictionary(GenericIndexedWriter<String> dictionaryWriter)

processing/src/main/java/org/apache/druid/segment/serde/DoubleNumericColumnPartSerde.java

@@ -23,14 +23,12 @@ import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.base.Supplier;
 import org.apache.druid.segment.IndexIO;
-import org.apache.druid.segment.column.ColumnBuilder;
-import org.apache.druid.segment.column.ColumnConfig;
 import org.apache.druid.segment.column.ValueType;
 import org.apache.druid.segment.data.ColumnarDoubles;
 import org.apache.druid.segment.data.CompressedColumnarDoublesSuppliers;
 
 import javax.annotation.Nullable;
-import java.nio.ByteBuffer;
+
 import java.nio.ByteOrder;
 
 public class DoubleNumericColumnPartSerde implements ColumnPartSerde
@@ -66,7 +64,9 @@ public class DoubleNumericColumnPartSerde implements ColumnPartSerde
 
   public static class SerializerBuilder
   {
+    @Nullable
     private ByteOrder byteOrder = null;
+    @Nullable
     private Serializer delegate = null;
 
     public SerializerBuilder withByteOrder(final ByteOrder byteOrder)
@@ -97,11 +97,7 @@ public class DoubleNumericColumnPartSerde implements ColumnPartSerde
   @Override
   public Deserializer getDeserializer()
   {
-    return new Deserializer()
+    return (buffer, builder, columnConfig) -> {
-    {
-      @Override
-      public void read(ByteBuffer buffer, ColumnBuilder builder, ColumnConfig columnConfig)
-      {
       final Supplier<ColumnarDoubles> column = CompressedColumnarDoublesSuppliers.fromByteBuffer(
           buffer,
           byteOrder
@@ -114,7 +110,6 @@ public class DoubleNumericColumnPartSerde implements ColumnPartSerde
              .setHasMultipleValues(false)
              .setNumericColumnSupplier(columnSupplier);
 
-      }
     };
   }
 }

processing/src/main/java/org/apache/druid/segment/serde/DoubleNumericColumnPartSerdeV2.java

@@ -54,7 +54,7 @@ public class DoubleNumericColumnPartSerdeV2 implements ColumnPartSerde
 
   private final ByteOrder byteOrder;
   @Nullable
-  private Serializer serializer;
+  private final Serializer serializer;
   private final BitmapSerdeFactory bitmapSerdeFactory;
 
   public DoubleNumericColumnPartSerdeV2(
@@ -87,8 +87,11 @@ public class DoubleNumericColumnPartSerdeV2 implements ColumnPartSerde
 
   public static class SerializerBuilder
   {
+    @Nullable
     private ByteOrder byteOrder = null;
+    @Nullable
     private Serializer delegate = null;
+    @Nullable
     private BitmapSerdeFactory bitmapSerdeFactory = null;
 
     public SerializerBuilder withByteOrder(final ByteOrder byteOrder)

processing/src/main/java/org/apache/druid/segment/serde/FloatNumericColumnPartSerde.java

@@ -66,7 +66,9 @@ public class FloatNumericColumnPartSerde implements ColumnPartSerde
 
   public static class SerializerBuilder
   {
+    @Nullable
     private ByteOrder byteOrder = null;
+    @Nullable
     private Serializer delegate = null;
 
     public SerializerBuilder withByteOrder(final ByteOrder byteOrder)

processing/src/main/java/org/apache/druid/segment/serde/FloatNumericColumnPartSerdeV2.java

@@ -52,7 +52,7 @@ public class FloatNumericColumnPartSerdeV2 implements ColumnPartSerde
 
   private final ByteOrder byteOrder;
   @Nullable
-  private Serializer serializer;
+  private final Serializer serializer;
   private final BitmapSerdeFactory bitmapSerdeFactory;
 
   private FloatNumericColumnPartSerdeV2(
@@ -85,8 +85,11 @@ public class FloatNumericColumnPartSerdeV2 implements ColumnPartSerde
 
   public static class SerializerBuilder
   {
+    @Nullable
     private ByteOrder byteOrder = null;
+    @Nullable
     private Serializer delegate = null;
+    @Nullable
     private BitmapSerdeFactory bitmapSerdeFactory = null;
 
     public SerializerBuilder withByteOrder(final ByteOrder byteOrder)

processing/src/main/java/org/apache/druid/segment/serde/LongNumericColumnPartSerde.java

@@ -22,13 +22,11 @@ package org.apache.druid.segment.serde;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import org.apache.druid.segment.IndexIO;
-import org.apache.druid.segment.column.ColumnBuilder;
-import org.apache.druid.segment.column.ColumnConfig;
 import org.apache.druid.segment.column.ValueType;
 import org.apache.druid.segment.data.CompressedColumnarLongsSupplier;
 
 import javax.annotation.Nullable;
-import java.nio.ByteBuffer;
+
 import java.nio.ByteOrder;
 
 /**
@@ -66,7 +64,9 @@ public class LongNumericColumnPartSerde implements ColumnPartSerde
 
   public static class SerializerBuilder
   {
+    @Nullable
     private ByteOrder byteOrder = null;
+    @Nullable
     private Serializer delegate = null;
 
     public SerializerBuilder withByteOrder(final ByteOrder byteOrder)
@@ -97,11 +97,7 @@ public class LongNumericColumnPartSerde implements ColumnPartSerde
   @Override
   public Deserializer getDeserializer()
   {
-    return new Deserializer()
+    return (buffer, builder, columnConfig) -> {
-    {
-      @Override
-      public void read(ByteBuffer buffer, ColumnBuilder builder, ColumnConfig columnConfig)
-      {
       final CompressedColumnarLongsSupplier column = CompressedColumnarLongsSupplier.fromByteBuffer(
           buffer,
           byteOrder
@@ -113,7 +109,6 @@ public class LongNumericColumnPartSerde implements ColumnPartSerde
       builder.setType(ValueType.LONG)
              .setHasMultipleValues(false)
              .setNumericColumnSupplier(columnSupplier);
-      }
     };
   }
 }

processing/src/main/java/org/apache/druid/segment/serde/LongNumericColumnPartSerdeV2.java

@@ -50,14 +50,16 @@ public class LongNumericColumnPartSerdeV2 implements ColumnPartSerde
     );
   }
 
+  @Nullable
+  private final Serializer serializer;
+  @Nullable
   private final ByteOrder byteOrder;
   @Nullable
-  private Serializer serializer;
   private final BitmapSerdeFactory bitmapSerdeFactory;
 
   private LongNumericColumnPartSerdeV2(
-      ByteOrder byteOrder,
+      @Nullable ByteOrder byteOrder,
-      BitmapSerdeFactory bitmapSerdeFactory,
+      @Nullable BitmapSerdeFactory bitmapSerdeFactory,
       @Nullable Serializer serializer
   )
   {
@@ -85,8 +87,11 @@ public class LongNumericColumnPartSerdeV2 implements ColumnPartSerde
 
   public static class SerializerBuilder
   {
+    @Nullable
     private ByteOrder byteOrder = null;
+    @Nullable
     private Serializer delegate = null;
+    @Nullable
     private BitmapSerdeFactory bitmapSerdeFactory = null;
 
     public SerializerBuilder withByteOrder(final ByteOrder byteOrder)

server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java

@@ -104,7 +104,7 @@ public class EventReceiverFirehoseFactory implements FirehoseFactory<InputRowPar
    * {@link EventReceiverFirehose} that may change in the future.
    */
   private final long maxIdleTimeMillis;
-  private final @Nullable ChatHandlerProvider chatHandlerProvider;
+  private final ChatHandlerProvider chatHandlerProvider;
   private final ObjectMapper jsonMapper;
   private final ObjectMapper smileMapper;
   private final EventReceiverFirehoseRegister eventReceiverFirehoseRegister;
@@ -225,6 +225,7 @@ public class EventReceiverFirehoseFactory implements FirehoseFactory<InputRowPar
      * This field and {@link #rowsRunOut} are not volatile because they are accessed only from {@link #hasMore()} and
      * {@link #nextRow()} methods that are called from a single thread according to {@link Firehose} spec.
      */
+    @Nullable
     private InputRow nextRow = null;
     private boolean rowsRunOut = false;
 
@@ -241,7 +242,9 @@ public class EventReceiverFirehoseFactory implements FirehoseFactory<InputRowPar
      * If they were not volatile, NPE would be possible in {@link #delayedCloseExecutor}. See
      * https://shipilev.net/blog/2016/close-encounters-of-jmm-kind/#wishful-hb-actual for explanations.
      */
+    @Nullable
     private volatile Long idleCloseTimeNs = null;
+    @Nullable
     private volatile Long requestedShutdownTimeNs = null;
 
     EventReceiverFirehose(InputRowParser<Map<String, Object>> parser)

server/src/main/java/org/apache/druid/segment/realtime/firehose/PredicateFirehose.java

@@ -40,6 +40,7 @@ public class PredicateFirehose implements Firehose
   private final Firehose firehose;
   private final Predicate<InputRow> predicate;
 
+  @Nullable
   private InputRow savedInputRow = null;
 
   public PredicateFirehose(Firehose firehose, Predicate<InputRow> predicate)

server/src/main/java/org/apache/druid/segment/realtime/firehose/SqlFirehoseFactory.java

@@ -35,6 +35,8 @@ import org.skife.jdbi.v2.exceptions.CallbackFailedException;
 import org.skife.jdbi.v2.exceptions.ResultSetException;
 import org.skife.jdbi.v2.exceptions.StatementException;
 
+import javax.annotation.Nullable;
+
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
@@ -51,6 +53,7 @@ public class SqlFirehoseFactory extends PrefetchSqlFirehoseFactory<String>
 {
   @JsonProperty
   private final List<String> sqls;
+  @Nullable
   @JsonProperty
   private final MetadataStorageConnectorConfig connectorConfig;
   private final ObjectMapper objectMapper;

server/src/main/java/org/apache/druid/server/coordination/BatchDataSegmentAnnouncer.java

@@ -69,7 +69,8 @@ public class BatchDataSegmentAnnouncer implements DataSegmentAnnouncer
   private final ConcurrentMap<DataSegment, SegmentZNode> segmentLookup = new ConcurrentHashMap<>();
   private final Function<DataSegment, DataSegment> segmentTransformer;
 
-  private final ChangeRequestHistory<DataSegmentChangeRequest> changes = new ChangeRequestHistory();
+  private final ChangeRequestHistory<DataSegmentChangeRequest> changes = new ChangeRequestHistory<>();
+  @Nullable
   private final SegmentZNode dummyZnode;
 
   @Inject
@@ -87,11 +88,7 @@ public class BatchDataSegmentAnnouncer implements DataSegmentAnnouncer
     this.server = server;
 
     this.liveSegmentLocation = ZKPaths.makePath(zkPaths.getLiveSegmentsPath(), server.getName());
-    segmentTransformer = new Function<DataSegment, DataSegment>()
+    segmentTransformer = input -> {
-    {
-      @Override
-      public DataSegment apply(DataSegment input)
-      {
       DataSegment rv = input;
       if (config.isSkipDimensionsAndMetrics()) {
         rv = rv.withDimensions(null).withMetrics(null);
@@ -100,7 +97,6 @@ public class BatchDataSegmentAnnouncer implements DataSegmentAnnouncer
         rv = rv.withLoadSpec(null);
       }
       return rv;
-      }
     };
 
     if (this.config.isSkipSegmentAnnouncementOnZk()) {

server/src/main/java/org/apache/druid/server/coordination/BatchDataSegmentAnnouncerProvider.java

@@ -21,15 +21,15 @@ package org.apache.druid.server.coordination;
 
 import com.fasterxml.jackson.annotation.JacksonInject;
 
-import javax.validation.constraints.NotNull;
+import javax.annotation.Nullable;
 
 /**
  */
 public class BatchDataSegmentAnnouncerProvider implements DataSegmentAnnouncerProvider
 {
   @JacksonInject
-  @NotNull
+  @Nullable
-  private BatchDataSegmentAnnouncer batchAnnouncer = null;
+  private final BatchDataSegmentAnnouncer batchAnnouncer = null;
 
   @Override
   public DataSegmentAnnouncer get()

server/src/main/java/org/apache/druid/server/coordination/ChangeRequestHttpSyncer.java

@@ -39,6 +39,7 @@ import org.jboss.netty.handler.codec.http.HttpHeaders;
 import org.jboss.netty.handler.codec.http.HttpMethod;
 import org.joda.time.Duration;
 
+import javax.annotation.Nullable;
 import javax.servlet.http.HttpServletResponse;
 import java.io.InputStream;
 import java.net.URL;
@@ -84,12 +85,14 @@ public class ChangeRequestHttpSyncer<T>
   private final LifecycleLock startStopLock = new LifecycleLock();
 
   private final String logIdentity;
-  private ChangeRequestHistory.Counter counter = null;
   private long unstableStartTime = -1;
   private int consecutiveFailedAttemptCount = 0;
   private long lastSuccessfulSyncTime = 0;
   private long lastSyncTime = 0;
 
+  @Nullable
+  private ChangeRequestHistory.Counter counter = null;
+
   public ChangeRequestHttpSyncer(
       ObjectMapper smileMapper,
       HttpClient httpClient,

server/src/main/java/org/apache/druid/server/coordination/SegmentLoadDropHandler.java

@@ -44,6 +44,8 @@ import org.apache.druid.segment.loading.SegmentLoadingException;
 import org.apache.druid.server.SegmentManager;
 import org.apache.druid.timeline.DataSegment;
 
+import javax.annotation.Nullable;
+
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
@@ -240,14 +242,7 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
 
     addSegments(
         cachedSegments,
-        new DataSegmentChangeCallback()
+        () -> log.info("Cache load took %,d ms", System.currentTimeMillis() - start)
-        {
-          @Override
-          public void execute()
-          {
-            log.info("Cache load took %,d ms", System.currentTimeMillis() - start);
-          }
-        }
     );
   }
 
@@ -348,11 +343,7 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
       final CopyOnWriteArrayList<DataSegment> failedSegments = new CopyOnWriteArrayList<>();
       for (final DataSegment segment : segments) {
         loadingExecutor.submit(
-            new Runnable()
+            () -> {
-            {
-              @Override
-              public void run()
-              {
               try {
                 log.info(
                     "Loading segment[%d/%d][%s]",
@@ -377,7 +368,6 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
                 latch.countDown();
               }
             }
-            }
         );
       }
 
@@ -427,11 +417,7 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
       announcer.unannounceSegment(segment);
       segmentsToDelete.add(segment);
 
-      Runnable runnable = new Runnable()
+      Runnable runnable = () -> {
-      {
-        @Override
-        public void run()
-        {
         try {
           synchronized (segmentDeleteLock) {
             if (segmentsToDelete.remove(segment)) {
@@ -449,7 +435,6 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
              .addData("segment", segment)
              .emit();
         }
-        }
       };
 
       if (scheduleDrop) {
@@ -543,7 +528,7 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
                 );
               }
             },
-            () -> resolveWaitingFutures()
+            this::resolveWaitingFutures
         );
       }
       return requestStatuses.getIfPresent(changeRequest);
@@ -588,7 +573,9 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
     private final Object lock = new Object();
 
     private volatile boolean finished = false;
+    @Nullable
     private volatile ScheduledFuture startedAnnouncing = null;
+    @Nullable
     private volatile ScheduledFuture nextAnnoucement = null;
 
     public BackgroundSegmentAnnouncer(
@@ -755,6 +742,7 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
     }
 
     private final STATE state;
+    @Nullable
     private final String failureCause;
 
     public static final Status SUCCESS = new Status(STATE.SUCCESS, null);
@@ -763,7 +751,7 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
     @JsonCreator
     Status(
         @JsonProperty("state") STATE state,
-        @JsonProperty("failureCause") String failureCause
+        @JsonProperty("failureCause") @Nullable String failureCause
     )
     {
       Preconditions.checkNotNull(state, "state must be non-null");
@@ -782,6 +770,7 @@ public class SegmentLoadDropHandler implements DataSegmentChangeHandler
       return state;
     }
 
+    @Nullable
     @JsonProperty
     public String getFailureCause()
     {

server/src/main/java/org/apache/druid/server/coordination/ZkCoordinator.java

@@ -25,8 +25,6 @@ import com.google.inject.Inject;
 import org.apache.curator.framework.CuratorFramework;
 import org.apache.curator.framework.recipes.cache.ChildData;
 import org.apache.curator.framework.recipes.cache.PathChildrenCache;
-import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
-import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener;
 import org.apache.curator.utils.ZKPaths;
 import org.apache.druid.java.util.common.concurrent.Execs;
 import org.apache.druid.java.util.common.lifecycle.LifecycleStart;
@@ -35,6 +33,8 @@ import org.apache.druid.java.util.emitter.EmittingLogger;
 import org.apache.druid.segment.loading.SegmentLoaderConfig;
 import org.apache.druid.server.initialization.ZkPathsConfig;
 
+import javax.annotation.Nullable;
+
 import java.io.IOException;
 import java.util.concurrent.ExecutorService;
 
@@ -54,6 +54,7 @@ public class ZkCoordinator
   private final DruidServerMetadata me;
   private final CuratorFramework curator;
 
+  @Nullable
   private volatile PathChildrenCache loadQueueCache;
   private volatile boolean started = false;
   private final ExecutorService segmentLoadUnloadService;
@@ -107,11 +108,7 @@ public class ZkCoordinator
         curator.newNamespaceAwareEnsurePath(liveSegmentsLocation).ensure(curator.getZookeeperClient());
 
         loadQueueCache.getListenable().addListener(
-            new PathChildrenCacheListener()
+            (client, event) -> {
-            {
-              @Override
-              public void childEvent(CuratorFramework client, PathChildrenCacheEvent event)
-              {
               final ChildData child = event.getData();
               switch (event.getType()) {
                 case CHILD_ADDED:
@@ -124,7 +121,6 @@ public class ZkCoordinator
                   log.info("Ignoring event[%s]", event);
               }
             }
-            }
 
         );
         loadQueueCache.start();
@@ -151,11 +147,7 @@ public class ZkCoordinator
 
         finalRequest.go(
             dataSegmentChangeHandler,
-            new DataSegmentChangeCallback()
+            () -> {
-            {
-              @Override
-              public void execute()
-              {
               try {
                 curator.delete().guaranteed().forPath(path);
                 log.info("Completed request [%s]", finalRequest.asString());
@@ -171,7 +163,6 @@ public class ZkCoordinator
                 throw new RuntimeException(e);
               }
             }
-            }
         );
       }
       catch (Exception e) {