Cleaning up Javadocs in core-ui classes.
Added common constants to AbstractCellFormatter.

Change-Id: Ie20ea62f059646e7d6c7f3660dd60a60c40532fe
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/HexLongFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/HexLongFormatter.java
index c5bb69d..67d0fa3 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/HexLongFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/HexLongFormatter.java
@@ -28,7 +28,7 @@
 
     @Override
     protected String nonNullFormat(Object value) {
-        return "0x" + Long.toHexString((Long) value);
+        return OX + Long.toHexString((Long) value);
     }
 
     /**