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/AbstractCellComparator.java b/core/api/src/main/java/org/onosproject/ui/table/cell/AbstractCellComparator.java
index b042c85..31f42ea 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/AbstractCellComparator.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/AbstractCellComparator.java
@@ -42,19 +42,17 @@
     /**
      * Compares its two arguments for order.  Returns a negative integer,
      * zero, or a positive integer as the first argument is less than, equal
-     * to, or greater than the second.<p>
-     *
+     * to, or greater than the second.
+     * <p>
      * Note that both objects are guaranteed to be non-null.
      *
      * @see java.util.Comparator#compare(Object, Object)
      *
-     * @param o1 the first object to be compared.
-     * @param o2 the second object to be compared.
-     * @return a negative integer, zero, or a positive integer as the
-     *         first argument is less than, equal to, or greater than the
-     *         second.
+     * @param o1 the first object to be compared
+     * @param o2 the second object to be compared
+     * @return an integer representing relative ordering
      * @throws ClassCastException if the arguments' types prevent them from
-     *         being compared by this comparator.
+     *         being compared by this comparator
      */
     protected abstract int nonNullCompare(Object o1, Object o2);
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/AbstractCellFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/AbstractCellFormatter.java
index 4329f14..3f3afc4 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/AbstractCellFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/AbstractCellFormatter.java
@@ -25,9 +25,17 @@
  */
 public abstract class AbstractCellFormatter implements CellFormatter {
 
+    protected static final String EMPTY = "";
+    protected static final String SLASH = "/";
+    protected static final String QUERY = "?";
+    protected static final String UNDERSCORE = "_";
+    protected static final String SPACE = " ";
+    protected static final String OX = "0x";
+
+
     @Override
     public String format(Object value) {
-        return value == null ? "" : nonNullFormat(value);
+        return value == null ? EMPTY : nonNullFormat(value);
     }
 
     /**
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java
index d44836f..9966a88 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java
@@ -24,6 +24,8 @@
  */
 public final class AppIdFormatter extends AbstractCellFormatter {
 
+    private static final String COLON = " : ";
+
     // non-instantiable
     private AppIdFormatter() { }
 
@@ -31,7 +33,7 @@
     @Override
     protected String nonNullFormat(Object value) {
         ApplicationId appId = (ApplicationId) value;
-        return appId.id() + " : " + appId.name();
+        return appId.id() + COLON + appId.name();
     }
 
     /**
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/ConnectPointFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/ConnectPointFormatter.java
index f64c296..7d9964f 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/ConnectPointFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/ConnectPointFormatter.java
@@ -30,7 +30,7 @@
     @Override
     protected String nonNullFormat(Object value) {
         ConnectPoint cp = (ConnectPoint) value;
-        return cp.elementId() + "/" + cp.port();
+        return cp.elementId() + SLASH + cp.port();
     }
 
     /**
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 e8e41e8..7a8d9aa 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
@@ -30,7 +30,7 @@
 
     @Override
     protected String nonNullFormat(Object value) {
-        return capitalizeFully(value.toString().replace("_", " "));
+        return capitalizeFully(value.toString().replace(UNDERSCORE, SPACE));
     }
 
     /**
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 e96a8be..4e3194b 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
@@ -28,7 +28,7 @@
 
     @Override
     protected String nonNullFormat(Object value) {
-        return "0x" + Integer.toHexString((Integer) value);
+        return OX + Integer.toHexString((Integer) value);
     }
 
     /**
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);
     }
 
     /**
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/HostLocationFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/HostLocationFormatter.java
index 306cea1..be652ca 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/HostLocationFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/HostLocationFormatter.java
@@ -30,7 +30,7 @@
     @Override
     protected String nonNullFormat(Object value) {
         HostLocation loc = (HostLocation) value;
-        return loc.deviceId() + "/" + loc.port();
+        return loc.deviceId() + SLASH + loc.port();
     }
 
     /**
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/NumberFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/NumberFormatter.java
index 597a8a4..93c0754 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/NumberFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/NumberFormatter.java
@@ -22,7 +22,7 @@
 import java.text.NumberFormat;
 
 /**
- * Formats number using the specified format string".
+ * Formats number using the specified format string.
  */
 public final class NumberFormatter extends AbstractCellFormatter {