Add some finals where appropriate

Author: s1monw

src/main/java/org/elasticsearch/cluster/ClusterState.java

@@ -92,7 +92,7 @@ interface Factory<T extends Custom> {
         }
     }
 
-    public static Map<String, Custom.Factory> customFactories = new HashMap<>();
+    private final static Map<String, Custom.Factory> customFactories = new HashMap<>();
 
     /**
      * Register a custom index meta data factory. Make sure to call it from a static block.

src/main/java/org/elasticsearch/index/fielddata/IndexFieldData.java

@@ -41,7 +41,7 @@
 public interface IndexFieldData<FD extends AtomicFieldData> extends IndexComponent {
 
     public static class CommonSettings {
-        public static String SETTING_MEMORY_STORAGE_HINT = "memory_storage_hint";
+        public static final String SETTING_MEMORY_STORAGE_HINT = "memory_storage_hint";
 
         public enum MemoryStorageFormat {
             ORDINALS, PACKED, PAGED;

src/main/java/org/elasticsearch/search/aggregations/BucketCollector.java

@@ -31,7 +31,7 @@
  */
 public abstract class BucketCollector implements ReaderContextAware {
 
-    public static BucketCollector NO_OP_COLLECTOR = new BucketCollector() {
+    public final static BucketCollector NO_OP_COLLECTOR = new BucketCollector() {
 
         @Override
         public void collect(int docId, long bucketOrdinal) throws IOException {