GUI -- Made OOTB formatters and comparators final classes.

Change-Id: I0ea59bf92d97b6d104b7d3770fb5f2e93308bbdc
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/EnumFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/EnumFormatter.java
index 7060e82..5b89a0b 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/EnumFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/EnumFormatter.java
@@ -23,7 +23,10 @@
 /**
  * Formats enum types to be readable strings.
  */
-public class EnumFormatter extends AbstractCellFormatter {
+public final class EnumFormatter extends AbstractCellFormatter {
+
+    // non-instantiable
+    private EnumFormatter() { }
 
     @Override
     protected String nonNullFormat(Object value) {