Make private static classes final

src/main/java/org/apache/commons/collections4/CollectionUtils.java

@@ -161,7 +161,7 @@ private int getFreq(final Object obj, final Map<?, Integer> freqMap) {
      * Helper class for set-related operations, e.g. union, subtract, intersection.
      * @param <O>  the element type
      */
-    private static class SetOperationCardinalityHelper<O> extends CardinalityHelper<O> implements Iterable<O> {
+    private static final class SetOperationCardinalityHelper<O> extends CardinalityHelper<O> implements Iterable<O> {
 
         /** Contains the unique elements of the two collections. */
         private final Set<O> elements;
@@ -712,7 +712,7 @@ public static <E> int hashCode(final Collection<? extends E> collection,
      * @param <O>  the element type
      * @since 4.0
      */
-    private static class EquatorWrapper<O> {
+    private static final class EquatorWrapper<O> {
         private final Equator<? super O> equator;
         private final O object;
 

src/main/java/org/apache/commons/collections4/ListUtils.java

@@ -98,7 +98,7 @@ public void visitKeepCommand(final E object) {
      * Provides a partition view on a {@link List}.
      * @since 4.0
      */
-    private static class Partition<T> extends AbstractList<List<T>> {
+    private static final class Partition<T> extends AbstractList<List<T>> {
         private final List<T> list;
         private final int size;
 

src/main/java/org/apache/commons/collections4/SplitMapUtils.java

@@ -44,7 +44,7 @@ public class SplitMapUtils {
     private SplitMapUtils() {}
 
 
-    private static class WrappedGet<K, V> implements IterableMap<K, V>, Unmodifiable {
+    private static final class WrappedGet<K, V> implements IterableMap<K, V>, Unmodifiable {
         private final Get<K, V> get;
 
         private WrappedGet(final Get<K, V> get) {
@@ -136,7 +136,7 @@ public MapIterator<K, V> mapIterator() {
         }
     }
 
-    private static class WrappedPut<K, V> implements Map<K, V>, Put<K, V> {
+    private static final class WrappedPut<K, V> implements Map<K, V>, Put<K, V> {
         private final Put<K, V> put;
 
         private WrappedPut(final Put<K, V> put) {

src/main/java/org/apache/commons/collections4/map/MultiValueMap.java

@@ -541,7 +541,7 @@ public V next() {
     /**
      * Inner class that provides a simple reflection factory.
      */
-    private static class ReflectionFactory<T extends Collection<?>> implements Factory<T>, Serializable {
+    private static final class ReflectionFactory<T extends Collection<?>> implements Factory<T>, Serializable {
 
         /** Serialization version */
         private static final long serialVersionUID = 2986114157496788874L;

src/main/java/org/apache/commons/collections4/multiset/AbstractMapMultiSet.java

@@ -147,7 +147,7 @@ public Iterator<E> iterator() {
     /**
      * Inner class iterator for the MultiSet.
      */
-    private static class MapBasedMultiSetIterator<E> implements Iterator<E> {
+    private static final class MapBasedMultiSetIterator<E> implements Iterator<E> {
         private final AbstractMapMultiSet<E> parent;
         private final Iterator<Map.Entry<E, MutableInteger>> entryIterator;
         private Map.Entry<E, MutableInteger> current;

src/main/java/org/apache/commons/collections4/multiset/AbstractMultiSet.java

@@ -122,7 +122,7 @@ public Iterator<E> iterator() {
     /**
      * Inner class iterator for the MultiSet.
      */
-    private static class MultiSetIterator<E> implements Iterator<E> {
+    private static final class MultiSetIterator<E> implements Iterator<E> {
         private final AbstractMultiSet<E> parent;
         private final Iterator<Entry<E>> entryIterator;
         private Entry<E> current;

src/main/java/org/apache/commons/collections4/properties/PropertiesFactory.java

@@ -43,7 +43,7 @@
  */
 public class PropertiesFactory extends AbstractPropertiesFactory<Properties> {
 
-    private static class EmptyProperties extends Properties {
+    private static final class EmptyProperties extends Properties {
 
         private static final long serialVersionUID = 1L;
 

src/main/java/org/apache/commons/collections4/sequence/SequencesComparator.java

@@ -292,7 +292,7 @@ private void buildScript(final int start1, final int end1, final int start2, fin
      * This class is a simple placeholder to hold the end part of a path
      * under construction in a {@link SequencesComparator SequencesComparator}.
      */
-    private static class Snake {
+    private static final class Snake {
 
         /** Start index. */
         private final int start;

src/main/java/org/apache/commons/collections4/trie/AbstractPatriciaTrie.java

@@ -1257,7 +1257,7 @@ static boolean isValidUplink(final TrieEntry<?, ?> next, final TrieEntry<?, ?> f
      * wise there's no difference (except for the need to load the
      * {@link Reference} Class but that happens only once).
      */
-    private static class Reference<E> {
+    private static final class Reference<E> {
 
         private E item;
 

src/test/java/org/apache/commons/collections4/MapPerformance.java

@@ -127,7 +127,7 @@ private static void test(final Map<String, String> map, final String name) {
         System.out.println(name + (endMillis - startMillis));
     }
 
-    private static class DummyMap<K, V> implements Map<K, V> {
+    private static final class DummyMap<K, V> implements Map<K, V> {
         @Override
         public void clear() {
         }

src/test/java/org/apache/commons/collections4/bidimap/DualTreeBidiMap2Test.java

@@ -97,7 +97,7 @@ public void testSerializeDeserializeCheckComparator() throws Exception {
         }
     }
 
-    private static class IntegerComparator implements Comparator<Integer>, Serializable{
+    private static final class IntegerComparator implements Comparator<Integer>, Serializable{
         private static final long serialVersionUID = 1L;
         @Override
         public int compare(final Integer o1, final Integer o2) {

src/test/java/org/apache/commons/collections4/bloomfilter/IndexProducerFromBitmapProducerTest.java

@@ -84,7 +84,7 @@ public final void testFromBitMapProducerTest() {
         }
     }
 
-    private static class TestingBitMapProducer implements BitMapProducer {
+    private static final class TestingBitMapProducer implements BitMapProducer {
         long[] values;
 
         TestingBitMapProducer(final long[] values) {

src/test/java/org/apache/commons/collections4/bloomfilter/IndexProducerTest.java

@@ -54,7 +54,7 @@ public void fromBitMapProducerTest() {
         }
     }
 
-    private static class TestingBitMapProducer implements BitMapProducer {
+    private static final class TestingBitMapProducer implements BitMapProducer {
         long[] values;
 
         TestingBitMapProducer(final long[] values) {

src/test/java/org/apache/commons/collections4/collection/PredicatedCollectionBuilderTest.java

@@ -129,7 +129,7 @@ private void checkPredicatedCollection2(final Collection<Integer> collection) {
         assertEquals(3, collection.size());
     }
 
-    private static class OddPredicate implements Predicate<Integer> {
+    private static final class OddPredicate implements Predicate<Integer> {
         @Override
         public boolean evaluate(final Integer value) {
             return value % 2 == 1;

src/test/java/org/apache/commons/collections4/collection/TransformedCollectionTest.java

@@ -38,14 +38,14 @@
  */
 public class TransformedCollectionTest extends AbstractCollectionTest<Object> {
 
-    private static class StringToInteger implements Transformer<Object, Object> {
+    private static final class StringToInteger implements Transformer<Object, Object> {
         @Override
         public Object transform(final Object input) {
             return Integer.valueOf((String) input);
         }
     }
 
-    private static class ToLowerCase implements Transformer<Object, Object> {
+    private static final class ToLowerCase implements Transformer<Object, Object> {
         @Override
         public Object transform(final Object input) {
             return ((String) input).toLowerCase();

src/test/java/org/apache/commons/collections4/functors/ComparatorPredicateTest.java

@@ -26,7 +26,7 @@
 
 
 public class ComparatorPredicateTest extends AbstractPredicateTest {
-    private static class TestComparator<T extends Comparable<T>> implements Comparator<T> {
+    private static final class TestComparator<T extends Comparable<T>> implements Comparator<T> {
         @Override
         public int compare(final T first, final T second) {
             return first.compareTo(second);

src/test/java/org/apache/commons/collections4/map/LazySortedMapTest.java

@@ -45,7 +45,7 @@
 @SuppressWarnings("boxing")
 public class LazySortedMapTest<K, V> extends AbstractSortedMapTest<K, V> {
 
-    private static class ReverseStringComparator implements Comparator<String> {
+    private static final class ReverseStringComparator implements Comparator<String> {
 
         @Override
         public int compare(final String arg0, final String arg1) {

src/test/java/org/apache/commons/collections4/map/PassiveExpiringMapTest.java

@@ -40,7 +40,7 @@
  */
 public class PassiveExpiringMapTest<K, V> extends AbstractMapTest<K, V> {
 
-    private static class TestExpirationPolicy
+    private static final class TestExpirationPolicy
         implements ExpirationPolicy<Integer, String> {
 
         private static final long serialVersionUID = 1L;

src/test/java/org/apache/commons/collections4/map/ReferenceMapTest.java

@@ -346,7 +346,7 @@ private static void gc() {
         }
     }
 
-    private static class AccessibleEntry<K, V> extends ReferenceEntry<K, V> {
+    private static final class AccessibleEntry<K, V> extends ReferenceEntry<K, V> {
         final AbstractReferenceMap<K, V> parent;
         final Consumer<V> consumer;
 

src/test/java/org/apache/commons/collections4/sequence/SequencesComparatorTest.java

@@ -154,7 +154,7 @@ private List<Character> sequence(final String string) {
         return list;
     }
 
-    private static class ExecutionVisitor<T> implements CommandVisitor<T> {
+    private static final class ExecutionVisitor<T> implements CommandVisitor<T> {
 
         private List<T> v;
         private int index;