Prohibit LinkedList

api/src/main/java/org/apache/druid/guice/LifecycleScope.java

@@ -19,13 +19,13 @@
 
 package org.apache.druid.guice;
 
-import com.google.common.collect.Lists;
 import com.google.inject.Key;
 import com.google.inject.Provider;
 import com.google.inject.Scope;
 import org.apache.druid.java.util.common.lifecycle.Lifecycle;
 import org.apache.druid.java.util.common.logger.Logger;
 
+import java.util.ArrayList;
 import java.util.List;
 
 /**
@@ -37,7 +37,7 @@ public class LifecycleScope implements Scope
   private final Lifecycle.Stage stage;
 
   private Lifecycle lifecycle;
-  private final List<Object> instances = Lists.newLinkedList();
+  private final List<Object> instances = new ArrayList<>();
 
   public LifecycleScope(Lifecycle.Stage stage)
   {

codestyle/druid-forbidden-apis.txt

@@ -4,4 +4,8 @@ com.google.common.util.concurrent.Futures#transform(com.google.common.util.concu
 com.google.common.collect.Iterators#emptyIterator() @ Use java.util.Collections#emptyIterator()
 com.google.common.base.Charsets @ Use java.nio.charset.StandardCharsets instead
 java.io.File#toURL() @ Use java.io.File#toURI() and java.net.URI#toURL() instead
-org.apache.commons.io.FileUtils#getTempDirectory() @ Use org.junit.rules.TemporaryFolder for tests instead
+org.apache.commons.io.FileUtils#getTempDirectory() @ Use org.junit.rules.TemporaryFolder for tests instead
+
+java.util.LinkedList @ Use ArrayList or ArrayDeque instead
+com.google.common.collect.Lists#newLinkedList() @ Use ArrayList or ArrayDeque instead
+com.google.common.collect.Lists#newLinkedList(java.lang.Iterable) @ Use ArrayList or ArrayDeque instead

extensions-core/histogram/src/test/java/org/apache/druid/query/aggregation/histogram/ApproximateHistogramTest.java

@@ -20,12 +20,12 @@
 package org.apache.druid.query.aggregation.histogram;
 
 import com.google.common.collect.Iterators;
-import com.google.common.collect.Lists;
 import org.apache.druid.java.util.common.StringUtils;
 import org.junit.Assert;
 import org.junit.Test;
 
 import java.nio.ByteBuffer;
+import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Random;
@@ -239,7 +239,7 @@ public void testFoldSpeed()
       randNums[i] = (float) rand.nextGaussian();
     }
 
-    List<ApproximateHistogram> randHist = Lists.newLinkedList();
+    List<ApproximateHistogram> randHist = new ArrayList<>();
     Iterator<ApproximateHistogram> it = Iterators.cycle(randHist);
 
     for (int k = 0; k < numRand; ++k) {

extensions-core/kafka-indexing-service/src/main/java/org/apache/druid/indexing/kafka/IncrementalPublishingKafkaIndexTaskRunner.java

@@ -99,11 +99,11 @@
 import java.io.File;
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -181,8 +181,8 @@ public class IncrementalPublishingKafkaIndexTaskRunner implements KafkaIndexTask
   private final RowIngestionMeters rowIngestionMeters;
 
   private final Set<String> publishingSequences = Sets.newConcurrentHashSet();
-  private final List<ListenableFuture<SegmentsAndMetadata>> publishWaitList = new LinkedList<>();
-  private final List<ListenableFuture<SegmentsAndMetadata>> handOffWaitList = new LinkedList<>();
+  private final List<ListenableFuture<SegmentsAndMetadata>> publishWaitList = new ArrayList<>();
+  private final List<ListenableFuture<SegmentsAndMetadata>> handOffWaitList = new ArrayList<>();
 
   private volatile DateTime startTime;
   private volatile Status status = Status.NOT_STARTED; // this is only ever set by the task runner thread (runThread)

hll/src/test/java/org/apache/druid/hll/HyperLogLogCollectorBenchmark.java

@@ -23,14 +23,14 @@
 import com.google.caliper.Runner;
 import com.google.caliper.SimpleBenchmark;
 import com.google.common.base.Preconditions;
-import com.google.common.collect.Lists;
 import com.google.common.hash.HashFunction;
 import com.google.common.hash.Hashing;
 import sun.misc.Unsafe;
 
 import java.lang.reflect.Field;
 import java.nio.Buffer;
 import java.nio.ByteBuffer;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
 
@@ -41,7 +41,7 @@ public class HyperLogLogCollectorBenchmark extends SimpleBenchmark
 {
   private final HashFunction fn = Hashing.murmur3_128();
 
-  private final List<HyperLogLogCollector> collectors = Lists.newLinkedList();
+  private final List<HyperLogLogCollector> collectors = new ArrayList<>();
 
   @Param({"true"}) boolean targetIsDirect;
   @Param({"default", "random", "0"}) String alignment;

indexing-service/src/test/java/org/apache/druid/indexing/common/task/AppenderatorDriverRealtimeIndexTaskTest.java

@@ -29,6 +29,7 @@
 import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.ListeningExecutorService;
 import com.google.common.util.concurrent.MoreExecutors;
+import org.apache.commons.io.FileUtils;
 import org.apache.druid.client.cache.CacheConfig;
 import org.apache.druid.client.cache.CachePopulatorStats;
 import org.apache.druid.client.cache.MapCache;
@@ -49,12 +50,12 @@
 import org.apache.druid.discovery.LookupNodeService;
 import org.apache.druid.indexer.IngestionState;
 import org.apache.druid.indexer.TaskState;
+import org.apache.druid.indexer.TaskStatus;
 import org.apache.druid.indexing.common.Counters;
 import org.apache.druid.indexing.common.IngestionStatsAndErrorsTaskReportData;
 import org.apache.druid.indexing.common.SegmentLoaderFactory;
 import org.apache.druid.indexing.common.TaskReport;
 import org.apache.druid.indexing.common.TaskReportFileWriter;
-import org.apache.druid.indexer.TaskStatus;
 import org.apache.druid.indexing.common.TaskToolbox;
 import org.apache.druid.indexing.common.TaskToolboxFactory;
 import org.apache.druid.indexing.common.TestUtils;
@@ -133,7 +134,6 @@
 import org.apache.druid.timeline.partition.LinearShardSpec;
 import org.apache.druid.timeline.partition.NumberedShardSpec;
 import org.apache.druid.utils.Runnables;
-import org.apache.commons.io.FileUtils;
 import org.easymock.EasyMock;
 import org.joda.time.DateTime;
 import org.joda.time.Period;
@@ -149,10 +149,11 @@
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
+import java.util.ArrayDeque;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.LinkedList;
+import java.util.Deque;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -178,7 +179,7 @@ public class AppenderatorDriverRealtimeIndexTaskTest
   private static class TestFirehose implements Firehose
   {
     private final InputRowParser<Map<String, Object>> parser;
-    private final List<Map<String, Object>> queue = new LinkedList<>();
+    private final Deque<Optional<Map<String, Object>>> queue = new ArrayDeque<>();
     private boolean closed = false;
 
     public TestFirehose(final InputRowParser<Map<String, Object>> parser)
@@ -189,7 +190,7 @@ public TestFirehose(final InputRowParser<Map<String, Object>> parser)
     public void addRows(List<Map<String, Object>> rows)
     {
       synchronized (this) {
-        queue.addAll(rows);
+        rows.stream().map(Optional::ofNullable).forEach(queue::add);
         notifyAll();
       }
     }
@@ -215,7 +216,7 @@ public boolean hasMore()
     public InputRow nextRow()
     {
       synchronized (this) {
-        final InputRow row = parser.parseBatch(queue.remove(0)).get(0);
+        final InputRow row = parser.parseBatch(queue.removeFirst().orElse(null)).get(0);
         if (row != null && row.getRaw(FAIL_DIM) != null) {
           throw new ParseException(FAIL_DIM);
         }

indexing-service/src/test/java/org/apache/druid/indexing/common/task/RealtimeIndexTaskTest.java

@@ -46,9 +46,9 @@
 import org.apache.druid.discovery.DruidNodeAnnouncer;
 import org.apache.druid.discovery.LookupNodeService;
 import org.apache.druid.indexer.TaskState;
+import org.apache.druid.indexer.TaskStatus;
 import org.apache.druid.indexing.common.Counters;
 import org.apache.druid.indexing.common.SegmentLoaderFactory;
-import org.apache.druid.indexer.TaskStatus;
 import org.apache.druid.indexing.common.TaskToolbox;
 import org.apache.druid.indexing.common.TaskToolboxFactory;
 import org.apache.druid.indexing.common.TestUtils;
@@ -138,10 +138,12 @@
 import javax.annotation.Nullable;
 import java.io.File;
 import java.nio.file.Files;
+import java.util.ArrayDeque;
 import java.util.Arrays;
-import java.util.LinkedList;
+import java.util.Deque;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutionException;
@@ -161,7 +163,7 @@ public class RealtimeIndexTaskTest
   private static class TestFirehose implements Firehose
   {
     private final InputRowParser<Map<String, Object>> parser;
-    private final List<Map<String, Object>> queue = new LinkedList<>();
+    private final Deque<Optional<Map<String, Object>>> queue = new ArrayDeque<>();
     private boolean closed = false;
 
     public TestFirehose(final InputRowParser<Map<String, Object>> parser)
@@ -172,7 +174,7 @@ public TestFirehose(final InputRowParser<Map<String, Object>> parser)
     public void addRows(List<Map<String, Object>> rows)
     {
       synchronized (this) {
-        queue.addAll(rows);
+        rows.stream().map(Optional::ofNullable).forEach(queue::add);
         notifyAll();
       }
     }
@@ -198,7 +200,7 @@ public boolean hasMore()
     public InputRow nextRow()
     {
       synchronized (this) {
-        final InputRow row = parser.parseBatch(queue.remove(0)).get(0);
+        final InputRow row = parser.parseBatch(queue.removeFirst().orElse(null)).get(0);
         if (row != null && row.getRaw(FAIL_DIM) != null) {
           throw new ParseException(FAIL_DIM);
         }

indexing-service/src/test/java/org/apache/druid/indexing/firehose/IngestSegmentFirehoseFactoryTest.java

@@ -110,7 +110,6 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -324,7 +323,7 @@ public DataSegment restore(DataSegment segment)
         null,
         new NoopTestTaskFileWriter()
     );
-    Collection<Object[]> values = new LinkedList<>();
+    Collection<Object[]> values = new ArrayList<>();
     for (InputRowParser parser : Arrays.<InputRowParser>asList(
         ROW_PARSER,
         new MapInputRowParser(

java-util/src/main/java/org/apache/druid/java/util/http/client/io/AppendableByteArrayInputStream.java

@@ -23,15 +23,16 @@
 
 import java.io.IOException;
 import java.io.InputStream;
-import java.util.LinkedList;
+import java.util.ArrayDeque;
+import java.util.Deque;
 
 /**
  */
 public class AppendableByteArrayInputStream extends InputStream
 {
   private static final Logger log = new Logger(AppendableByteArrayInputStream.class);
 
-  private final LinkedList<byte[]> bytes = new LinkedList<byte[]>();
+  private final Deque<byte[]> bytes = new ArrayDeque<>();
   private final SingleByteReaderDoer singleByteReaderDoer = new SingleByteReaderDoer();
 
   private volatile boolean done = false;

processing/src/main/java/org/apache/druid/query/aggregation/AggregatorUtil.java

@@ -37,8 +37,9 @@
 import org.apache.druid.segment.LongColumnSelector;
 import org.apache.druid.segment.virtual.ExpressionSelectors;
 
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashSet;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Set;
 
@@ -113,18 +114,20 @@ public class AggregatorUtil
    */
   public static List<PostAggregator> pruneDependentPostAgg(List<PostAggregator> postAggregatorList, String postAggName)
   {
-    LinkedList<PostAggregator> rv = Lists.newLinkedList();
+    ArrayList<PostAggregator> rv = new ArrayList<>();
     Set<String> deps = new HashSet<>();
     deps.add(postAggName);
-    // Iterate backwards to find the last calculated aggregate and add dependent aggregator as we find dependencies in reverse order
+    // Iterate backwards to find the last calculated aggregate and add dependent aggregator as we find dependencies
+    // in reverse order
     for (PostAggregator agg : Lists.reverse(postAggregatorList)) {
       if (deps.contains(agg.getName())) {
-        rv.addFirst(agg); // add to the beginning of List
+        rv.add(agg); // add to the beginning of List
         deps.remove(agg.getName());
         deps.addAll(agg.getDependentFields());
       }
     }
 
+    Collections.reverse(rv);
     return rv;
   }
 
@@ -135,10 +138,7 @@ public static Pair<List<AggregatorFactory>, List<PostAggregator>> condensedAggre
   )
   {
 
-    List<PostAggregator> condensedPostAggs = AggregatorUtil.pruneDependentPostAgg(
-        postAggList,
-        metric
-    );
+    List<PostAggregator> condensedPostAggs = AggregatorUtil.pruneDependentPostAgg(postAggList, metric);
     // calculate dependent aggregators for these postAgg
     Set<String> dependencySet = new HashSet<>();
     dependencySet.add(metric);
@@ -152,7 +152,7 @@ public static Pair<List<AggregatorFactory>, List<PostAggregator>> condensedAggre
         condensedAggs.add(aggregatorSpec);
       }
     }
-    return new Pair(condensedAggs, condensedPostAggs);
+    return new Pair<>(condensedAggs, condensedPostAggs);
   }
 
   public static BaseFloatColumnValueSelector makeColumnValueSelectorWithFloatDefault(

processing/src/main/java/org/apache/druid/query/topn/AggregateTopNMetricFirstAlgorithm.java

@@ -75,11 +75,8 @@ public void run(
   )
   {
     final String metric = query.getTopNMetricSpec().getMetricName(query.getDimensionSpec());
-    Pair<List<AggregatorFactory>, List<PostAggregator>> condensedAggPostAggPair = AggregatorUtil.condensedAggregators(
-        query.getAggregatorSpecs(),
-        query.getPostAggregatorSpecs(),
-        metric
-    );
+    Pair<List<AggregatorFactory>, List<PostAggregator>> condensedAggPostAggPair =
+        AggregatorUtil.condensedAggregators(query.getAggregatorSpecs(), query.getPostAggregatorSpecs(), metric);
 
     if (condensedAggPostAggPair.lhs.isEmpty() && condensedAggPostAggPair.rhs.isEmpty()) {
       throw new ISE("WTF! Can't find the metric to do topN over?");

processing/src/main/java/org/apache/druid/query/topn/TopNQueryBuilder.java

@@ -37,7 +37,9 @@
 import org.apache.druid.segment.VirtualColumns;
 import org.joda.time.Interval;
 
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 
@@ -247,13 +249,13 @@ public TopNQueryBuilder granularity(Granularity g)
   @SuppressWarnings("unchecked")
   public TopNQueryBuilder aggregators(List<? extends AggregatorFactory> a)
   {
-    aggregatorSpecs = (List<AggregatorFactory>) a;
+    aggregatorSpecs = new ArrayList<>(a); // defensive copy
     return this;
   }
 
-  public TopNQueryBuilder postAggregators(List<PostAggregator> p)
+  public TopNQueryBuilder postAggregators(Collection<PostAggregator> p)
   {
-    postAggregatorSpecs = p;
+    postAggregatorSpecs = new ArrayList<>(p); // defensive copy
     return this;
   }
 

processing/src/test/java/org/apache/druid/query/aggregation/AggregatorUtilTest.java

@@ -172,11 +172,12 @@ public void testNullPostAggregatorNames()
     );
 
     Assert.assertEquals(
-        new Pair(Lists.newArrayList(agg1, agg2), Collections.singletonList(postAgg2)), AggregatorUtil.condensedAggregators(
-        Lists.newArrayList(agg1, agg2),
-        Lists.newArrayList(postAgg1, postAgg2),
-        "postAgg"
-    )
+        new Pair<>(Lists.newArrayList(agg1, agg2), Collections.singletonList(postAgg2)),
+        AggregatorUtil.condensedAggregators(
+            Lists.newArrayList(agg1, agg2),
+            Lists.newArrayList(postAgg1, postAgg2),
+            "postAgg"
+        )
     );
 
   }