GUI -- Made OOTB formatters and comparators final classes.

Change-Id: I0ea59bf92d97b6d104b7d3770fb5f2e93308bbdc
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/HexFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/HexFormatter.java
index 8104f48..e09982e 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/HexFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/HexFormatter.java
@@ -22,7 +22,10 @@
 /**
  * Formats integer values as hex strings with a "0x" prefix.
  */
-public class HexFormatter extends AbstractCellFormatter {
+public final class HexFormatter extends AbstractCellFormatter {
+
+    // non-instantiable
+    private HexFormatter() { }
 
     @Override
     protected String nonNullFormat(Object value) {