Cleanup and clarify usage of empty iterable and empty set

Use default available emptySet, use default empty iterator, clarify usage of empty iterator and empty resource iterator.
neo4j · May 9, 2017 · 998b3b0 · 998b3b0
1 parent c4fe909
commit 998b3b0
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Showing 34 changed files with 93 additions and 154 deletions.
diff --git a/community/collections/src/main/java/org/neo4j/helpers/collection/Iterables.java b/community/collections/src/main/java/org/neo4j/helpers/collection/Iterables.java
@@ -54,7 +54,7 @@ private Iterables()
     @SuppressWarnings( "unchecked" )
     public static <T> Iterable<T> empty()
     {
-        return EMPTY;
+        return Collections.emptyList();
     }
 
     public static <T> Iterable<T> limit( final int limitItems, final Iterable<T> iterable )
@@ -186,7 +186,7 @@ public static <X> Iterable<X> skip( final int skip, final Iterable<X> iterable )
                 }
                 else
                 {
-                    return Iterables.<X>empty().iterator();
+                    return Collections.emptyIterator();
                 }
             }
 
@@ -914,33 +914,4 @@ public static <T extends Enum<T>> List<String> enumNames( Class<T> cls )
         EnumSet.allOf( cls ).forEach( item -> names.add( item.name() ) );
         return names;
     }
-
-    private static Iterable EMPTY = new Iterable()
-    {
-        Iterator iterator = new Iterator()
-        {
-            @Override
-            public boolean hasNext()
-            {
-                return false;
-            }
-
-            @Override
-            public Object next()
-            {
-                throw new NoSuchElementException();
-            }
-
-            @Override
-            public void remove()
-            {
-            }
-        };
-
-        @Override
-        public Iterator iterator()
-        {
-            return iterator;
-        }
-    };
 }
diff --git a/community/collections/src/main/java/org/neo4j/helpers/collection/Iterators.java b/community/collections/src/main/java/org/neo4j/helpers/collection/Iterators.java
@@ -23,7 +23,6 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Deque;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -45,12 +44,17 @@
 import org.neo4j.graphdb.ResourceIterable;
 import org.neo4j.graphdb.ResourceIterator;
 
+import static java.util.Collections.emptyIterator;
+
 /**
  * Contains common functionality regarding {@link Iterator}s and
  * {@link Iterable}s.
  */
 public abstract class Iterators
 {
+    private static final ResourceIterator EMPTY_RESOURCE_ITERATOR =
+            resourceIterator( emptyIterator(), Resource.EMPTY );
+
     /**
      * Returns the given iterator's first element or {@code null} if no
      * element found.
@@ -421,11 +425,6 @@ public static <T> Set<T> asSet( T... items )
         return new HashSet<>( Arrays.asList( items ) );
     }
 
-    public static <T> Set<T> emptySetOf( @SuppressWarnings( "unused"/*just used as a type marker*/ ) Class<T> type )
-    {
-        return Collections.emptySet();
-    }
-
     /**
      * Alias for asSet()
      *
@@ -588,9 +587,9 @@ public static <T> Iterator<T> iterator( int maxItems, T ... items )
     }
 
     @SuppressWarnings( "unchecked" )
-    public static <T> ResourceIterator<T> emptyIterator()
+    public static <T> ResourceIterator<T> emptyResourceIterator()
     {
-        return EMPTY_ITERATOR;
+        return EMPTY_RESOURCE_ITERATOR;
     }
 
     public static <T> boolean contains( Iterator<T> iterator, T item )
@@ -648,34 +647,6 @@ public static <T> T[] array( T... items )
         return items;
     }
 
-    @SuppressWarnings( "rawtypes" )
-    private static final ResourceIterator EMPTY_ITERATOR = new ResourceIterator()
-    {
-        @Override
-        public boolean hasNext()
-        {
-            return false;
-        }
-
-        @Override
-        public Object next()
-        {
-            throw new NoSuchElementException();
-        }
-
-        @Override
-        public void remove()
-        {
-            throw new UnsupportedOperationException();
-        }
-
-        @Override
-        public void close()
-        {
-            // do nothing
-        }
-    };
-
     public static <X> Iterator<X> filter( Predicate<? super X> specification, Iterator<X> i )
     {
         return new FilterIterable.FilterIterator<>( i, specification );

diff --git a/community/kernel/src/main/java/org/neo4j/kernel/api/index/IndexAccessor.java b/community/kernel/src/main/java/org/neo4j/kernel/api/index/IndexAccessor.java
@@ -31,7 +31,8 @@
 import org.neo4j.kernel.impl.api.index.updater.SwallowingIndexUpdater;
 import org.neo4j.storageengine.api.schema.IndexReader;
 
-import static org.neo4j.helpers.collection.Iterators.emptyIterator;
+import static java.util.Collections.emptyIterator;
+import static org.neo4j.helpers.collection.Iterators.emptyResourceIterator;
 
 /**
  * Used for online operation of an index.
@@ -163,7 +164,7 @@ public Iterator<Long> iterator()
         @Override
         public ResourceIterator<File> snapshotFiles()
         {
-            return emptyIterator();
+            return emptyResourceIterator();
         }
 
         @Override

diff --git a/community/kernel/src/main/java/org/neo4j/kernel/api/index/SchemaIndexProvider.java b/community/kernel/src/main/java/org/neo4j/kernel/api/index/SchemaIndexProvider.java
@@ -229,7 +229,7 @@ public abstract StoreMigrationParticipant storeMigrationParticipant( FileSystemA
      */
     public ResourceIterator<File> snapshotMetaFiles()
     {
-        return Iterators.emptyIterator();
+        return Iterators.emptyResourceIterator();
     }
 
     public static class Descriptor

diff --git a/community/kernel/src/main/java/org/neo4j/kernel/impl/api/index/FailedIndexProxy.java b/community/kernel/src/main/java/org/neo4j/kernel/impl/api/index/FailedIndexProxy.java
@@ -33,7 +33,7 @@
 import org.neo4j.logging.LogProvider;
 
 import static org.neo4j.helpers.FutureAdapter.VOID;
-import static org.neo4j.helpers.collection.Iterators.emptyIterator;
+import static org.neo4j.helpers.collection.Iterators.emptyResourceIterator;
 
 public class FailedIndexProxy extends AbstractSwallowingIndexProxy
 {
@@ -95,6 +95,6 @@ public void validate() throws IndexPopulationFailedKernelException
     @Override
     public ResourceIterator<File> snapshotFiles()
     {
-        return emptyIterator();
+        return emptyResourceIterator();
     }
 }
diff --git a/community/kernel/src/main/java/org/neo4j/kernel/impl/api/index/PopulatingIndexProxy.java b/community/kernel/src/main/java/org/neo4j/kernel/impl/api/index/PopulatingIndexProxy.java
@@ -38,7 +38,7 @@
 import org.neo4j.storageengine.api.schema.IndexReader;
 import org.neo4j.storageengine.api.schema.PopulationProgress;
 
-import static org.neo4j.helpers.collection.Iterators.emptyIterator;
+import static org.neo4j.helpers.collection.Iterators.emptyResourceIterator;
 
 public class PopulatingIndexProxy implements IndexProxy
 {
@@ -157,7 +157,7 @@ public void validate()
     @Override
     public ResourceIterator<File> snapshotFiles()
     {
-        return emptyIterator();
+        return emptyResourceIterator();
     }
 
     @Override

diff --git a/...nity/kernel/src/main/java/org/neo4j/kernel/impl/api/state/PropertyContainerStateImpl.java b/...nity/kernel/src/main/java/org/neo4j/kernel/impl/api/state/PropertyContainerStateImpl.java
@@ -22,7 +22,6 @@
 import java.util.Iterator;
 import java.util.function.Predicate;
 
-import org.neo4j.graphdb.ResourceIterator;
 import org.neo4j.helpers.collection.CombiningIterator;
 import org.neo4j.helpers.collection.FilteringIterator;
 import org.neo4j.helpers.collection.Iterators;
@@ -32,12 +31,11 @@
 import org.neo4j.storageengine.api.StorageProperty;
 import org.neo4j.storageengine.api.txstate.PropertyContainerState;
 
-import static org.neo4j.helpers.collection.Iterators.emptyIterator;
+import static java.util.Collections.emptyIterator;
 
 public class PropertyContainerStateImpl implements PropertyContainerState
 {
     private final long id;
-    private static final ResourceIterator<StorageProperty> NO_PROPERTIES = emptyIterator();
 
     private VersionedHashMap<Integer, StorageProperty> addedProperties;
     private VersionedHashMap<Integer, StorageProperty> changedProperties;
@@ -145,20 +143,20 @@ public void removeProperty( DefinedProperty property )
     @Override
     public Iterator<StorageProperty> addedProperties()
     {
-        return addedProperties != null ? addedProperties.values().iterator() : NO_PROPERTIES;
+        return addedProperties != null ? addedProperties.values().iterator() : emptyIterator();
     }
 
     @Override
     public Iterator<StorageProperty> changedProperties()
     {
-        return changedProperties != null ? changedProperties.values().iterator() : NO_PROPERTIES;
+        return changedProperties != null ? changedProperties.values().iterator() : emptyIterator();
     }
 
     @Override
     public Iterator<Integer> removedProperties()
     {
         return removedProperties != null ? removedProperties.keySet().iterator()
-                : Iterators.<Integer>emptyIterator();
+                : emptyIterator();
     }
 
     @Override
@@ -181,7 +179,7 @@ public Iterator<StorageProperty> addedAndChangedProperties()
                 out = changedProperties.values().iterator();
             }
         }
-        return out != null ? out : NO_PROPERTIES;
+        return out != null ? out : emptyIterator();
     }
 
     @Override

diff --git a/community/kernel/src/main/java/org/neo4j/kernel/impl/api/store/SchemaCache.java b/community/kernel/src/main/java/org/neo4j/kernel/impl/api/store/SchemaCache.java
@@ -42,6 +42,8 @@
 import org.neo4j.kernel.impl.store.record.IndexRule;
 import org.neo4j.storageengine.api.schema.SchemaRule;
 
+import static java.util.Collections.emptyIterator;
+
 /**
  * A cache of {@link SchemaRule schema rules} as well as enforcement of schema consistency.
  * Will always reflect the committed state of the schema store.
@@ -237,12 +239,12 @@ public IndexDescriptor indexDescriptor( LabelSchemaDescriptor descriptor )
     public Iterator<IndexDescriptor> indexDescriptorsForLabel( int labelId )
     {
         Set<IndexDescriptor> forLabel = indexDescriptorsByLabel.get( labelId );
-        return forLabel == null ? Iterators.emptyIterator() : forLabel.iterator();
+        return forLabel == null ? emptyIterator() : forLabel.iterator();
     }
 
     public Iterator<IndexDescriptor> indexesByProperty( int propertyId )
     {
         List<IndexDescriptor> indexes = indexByProperty.get( propertyId );
-        return (indexes == null) ? Iterators.emptyIterator() : indexes.iterator();
+        return (indexes == null) ? emptyIterator() : indexes.iterator();
     }
 }
diff --git a/community/kernel/src/main/java/org/neo4j/kernel/impl/factory/GraphDatabaseFacade.java b/community/kernel/src/main/java/org/neo4j/kernel/impl/factory/GraphDatabaseFacade.java
@@ -108,7 +108,7 @@
 
 import static java.lang.String.format;
 import static org.neo4j.collection.primitive.PrimitiveLongCollections.map;
-import static org.neo4j.helpers.collection.Iterators.emptyIterator;
+import static org.neo4j.helpers.collection.Iterators.emptyResourceIterator;
 import static org.neo4j.kernel.api.security.SecurityContext.AUTH_DISABLED;
 import static org.neo4j.kernel.impl.api.legacyindex.InternalAutoIndexing.NODE_AUTO_INDEX;
 import static org.neo4j.kernel.impl.api.legacyindex.InternalAutoIndexing.RELATIONSHIP_AUTO_INDEX;
@@ -593,7 +593,7 @@ private ResourceIterator<Node> nodesByLabelAndProperty( Label myLabel, String ke
         if ( propertyId == NO_SUCH_PROPERTY_KEY || labelId == NO_SUCH_LABEL )
         {
             statement.close();
-            return emptyIterator();
+            return emptyResourceIterator();
         }
 
         IndexDescriptor descriptor = findAnyIndexByLabelAndProperty( readOps, propertyId, labelId );
@@ -652,7 +652,7 @@ private ResourceIterator<Node> allNodesWithLabel( final Label myLabel )
         if ( labelId == KeyReadOperations.NO_SUCH_LABEL )
         {
             statement.close();
-            return emptyIterator();
+            return emptyResourceIterator();
         }
 
         final PrimitiveLongIterator nodeIds = statement.readOperations().nodesGetForLabel( labelId );

diff --git a/...c/main/java/org/neo4j/kernel/impl/transaction/state/storeview/StoreViewNodeStoreScan.java b/...c/main/java/org/neo4j/kernel/impl/transaction/state/storeview/StoreViewNodeStoreScan.java
@@ -26,13 +26,12 @@
 import java.util.function.IntPredicate;
 
 import org.neo4j.collection.primitive.PrimitiveLongResourceIterator;
-import org.neo4j.helpers.collection.Iterators;
 import org.neo4j.helpers.collection.PrefetchingIterator;
 import org.neo4j.helpers.collection.Visitor;
 import org.neo4j.kernel.api.index.IndexEntryUpdate;
-import org.neo4j.kernel.impl.api.index.NodeUpdates;
 import org.neo4j.kernel.api.labelscan.NodeLabelUpdate;
 import org.neo4j.kernel.impl.api.index.MultipleIndexPopulator;
+import org.neo4j.kernel.impl.api.index.NodeUpdates;
 import org.neo4j.kernel.impl.locking.LockService;
 import org.neo4j.kernel.impl.store.NodeStore;
 import org.neo4j.kernel.impl.store.PropertyStore;
@@ -42,6 +41,7 @@
 import org.neo4j.kernel.impl.store.record.Record;
 import org.neo4j.kernel.impl.util.Validators;
 
+import static java.util.Collections.emptyIterator;
 import static org.neo4j.collection.primitive.PrimitiveLongCollections.EMPTY_LONG_ARRAY;
 import static org.neo4j.kernel.api.labelscan.NodeLabelUpdate.labelChanges;
 import static org.neo4j.kernel.impl.store.NodeLabelsField.parseLabelsField;
@@ -161,14 +161,14 @@ public void configure( Collection<MultipleIndexPopulator.IndexPopulation> popula
     private class PropertyBlockIterator extends PrefetchingIterator<PropertyBlock>
     {
         private final Iterator<PropertyRecord> records;
-        private Iterator<PropertyBlock> blocks = Iterators.emptyIterator();
+        private Iterator<PropertyBlock> blocks = emptyIterator();
 
         PropertyBlockIterator( NodeRecord node )
         {
             long firstPropertyId = node.getNextProp();
             if ( firstPropertyId == Record.NO_NEXT_PROPERTY.intValue() )
             {
-                records = Iterators.emptyIterator();
+                records = emptyIterator();
             }
             else
             {

diff --git a/...nity/kernel/src/main/java/org/neo4j/storageengine/api/txstate/PropertyContainerState.java b/...nity/kernel/src/main/java/org/neo4j/storageengine/api/txstate/PropertyContainerState.java
@@ -21,10 +21,11 @@
 
 import java.util.Iterator;
 
-import org.neo4j.helpers.collection.Iterators;
 import org.neo4j.kernel.api.exceptions.schema.ConstraintValidationException;
 import org.neo4j.storageengine.api.StorageProperty;
 
+import static java.util.Collections.emptyIterator;
+
 /**
  * Represents the property changes to a {@link NodeState node} or {@link RelationshipState relationship}:
  * <ul>
@@ -69,25 +70,25 @@ class EmptyPropertyContainerState implements PropertyContainerState
         @Override
         public Iterator<StorageProperty> addedProperties()
         {
-            return Iterators.emptyIterator();
+            return emptyIterator();
         }
 
         @Override
         public Iterator<StorageProperty> changedProperties()
         {
-            return Iterators.emptyIterator();
+            return emptyIterator();
         }
 
         @Override
         public Iterator<Integer> removedProperties()
         {
-            return Iterators.emptyIterator();
+            return emptyIterator();
         }
 
         @Override
         public Iterator<StorageProperty> addedAndChangedProperties()
         {
-            return Iterators.emptyIterator();
+            return emptyIterator();
         }
 
         @Override