GUI -- Made OOTB formatters and comparators final classes.

Change-Id: I0ea59bf92d97b6d104b7d3770fb5f2e93308bbdc
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/TimeFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/TimeFormatter.java
index e0aec9d..cdfdf3d 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/TimeFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/TimeFormatter.java
@@ -25,10 +25,13 @@
 /**
  * Formats time values using {@link DateTimeFormatter}.
  */
-public class TimeFormatter extends AbstractCellFormatter {
+public final class TimeFormatter extends AbstractCellFormatter {
 
     private static final DateTimeFormatter DTF = DateTimeFormat.longTime();
 
+    // non-instantiable
+    private TimeFormatter() { }
+
     @Override
     protected String nonNullFormat(Object value) {
         return DTF.print((DateTime) value);