diff --git a/core/api/src/main/java/org/onosproject/ui/chart/ChartModel.java b/core/api/src/main/java/org/onosproject/ui/chart/ChartModel.java
index b15705d..1cfb395 100644
--- a/core/api/src/main/java/org/onosproject/ui/chart/ChartModel.java
+++ b/core/api/src/main/java/org/onosproject/ui/chart/ChartModel.java
@@ -35,9 +35,9 @@
  * A simple model of time series chart data.
  * <p>
  * Note that this is not a full MVC type model; the expected usage pattern
- * is to create an empty chart, add data points (by consulting the business model),
- * and produce the list of data points which contain a label and a set of data
- * values for all serials.
+ * is to create an empty chart, add data points (by consulting the business
+ * model), and produce the list of data points which contain a label and a set
+ * of data values for all serials.
  */
 public class ChartModel {
 
diff --git a/core/api/src/main/java/org/onosproject/ui/chart/ChartRequestHandler.java b/core/api/src/main/java/org/onosproject/ui/chart/ChartRequestHandler.java
index 1d00689..5c3e2f7 100644
--- a/core/api/src/main/java/org/onosproject/ui/chart/ChartRequestHandler.java
+++ b/core/api/src/main/java/org/onosproject/ui/chart/ChartRequestHandler.java
@@ -27,11 +27,11 @@
  */
 public abstract class ChartRequestHandler extends RequestHandler {
 
+    protected static final String LABEL = "label";
+    private static final String ANNOTS = "annots";
+
     private final String respType;
     private final String nodeName;
-    protected static final String LABEL = "label";
-
-    private static final String ANNOTS = "annots";
 
     /**
      * Constructs a chart model handler for a specific graph view. When chart
@@ -56,7 +56,7 @@
         ObjectNode rootNode = MAPPER.createObjectNode();
         rootNode.set(nodeName, ChartUtils.generateDataPointArrayNode(cm));
         rootNode.set(ANNOTS, ChartUtils.generateAnnotObjectNode(cm));
-        sendMessage(respType, 0, rootNode);
+        sendMessage(respType, rootNode);
     }
 
     /**
@@ -72,8 +72,8 @@
         List<String> series = new ArrayList<>();
         series.addAll(Arrays.asList(getSeries()));
         series.add(LABEL);
-        String[] seiresArray = new String[series.size()];
-        return new ChartModel(series.toArray(seiresArray));
+        String[] array = new String[series.size()];
+        return new ChartModel(series.toArray(array));
     }
 
     /**
diff --git a/core/api/src/main/java/org/onosproject/ui/chart/package-info.java b/core/api/src/main/java/org/onosproject/ui/chart/package-info.java
index 5f85e03..4d1ce8e 100644
--- a/core/api/src/main/java/org/onosproject/ui/chart/package-info.java
+++ b/core/api/src/main/java/org/onosproject/ui/chart/package-info.java
@@ -15,6 +15,6 @@
  */
 
 /**
- * Facilities for creating chart models of data for the GUI.
+ * Facilities for creating chart models of data for the Web UI.
  */
 package org.onosproject.ui.chart;
\ No newline at end of file
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java
index d8803ab..f0aae01 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java
@@ -43,7 +43,7 @@
      * topology instance and the specified controller node instance.
      *
      * @param topology parent topology containing this cluster member
-     * @param cnode    underlying controller node.
+     * @param cnode    underlying controller node
      */
     public UiClusterMember(UiTopology topology, ControllerNode cnode) {
         this.topology = topology;
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
index c05d27b..04eaab0 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
@@ -101,7 +101,7 @@
      * Returns the identifier of the region to which this device belongs.
      * This will be null if the device does not belong to any region.
      *
-     * @return region identity
+     * @return region ID
      */
     public RegionId regionId() {
         return regionId;
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLayer.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLayer.java
deleted file mode 100644
index 30d16f6..0000000
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLayer.java
+++ /dev/null
@@ -1,34 +0,0 @@
-/*
- * Copyright 2016-present Open Networking Laboratory
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.onosproject.ui.model.topo;
-
-/**
- * Designates the logical layer of the network that an element belongs to.
- */
-public enum UiLayer {
-    PACKET, OPTICAL;
-
-    /**
-     * Returns the default layer (for those elements that do not explicitly
-     * define which layer they belong to).
-     *
-     * @return default layer
-     */
-    public static UiLayer defaultLayer() {
-        return PACKET;
-    }
-}
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLinkId.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLinkId.java
index 3bde82a..ca85fb2 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLinkId.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLinkId.java
@@ -49,7 +49,7 @@
         B_TO_A
     }
 
-    static final String CP_DELIMITER = "~";
+    private static final String CP_DELIMITER = "~";
     static final String ID_PORT_DELIMITER = "/";
 
     private final RegionId regionA;
@@ -236,7 +236,8 @@
         ConnectPoint src = link.src();
         ConnectPoint dst = link.dst();
         if (src == null || dst == null) {
-            throw new NullPointerException("null src or dst connect point: " + link);
+            throw new NullPointerException(
+                    "null src or dst connect point: " + link);
         }
 
         ElementId srcId = src.elementId();
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegionLink.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegionLink.java
index 45a27b9..afc6777 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegionLink.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegionLink.java
@@ -36,7 +36,7 @@
      * link identifier is one that has region IDs as source and destination.
      *
      * @param topology parent topology
-     * @param id       canonicalized link identifier
+     * @param id       canonicalized link ID
      * @throws IllegalArgumentException if the link ID is not region-region
      */
     public UiRegionLink(UiTopology topology, UiLinkId id) {
diff --git a/core/api/src/main/java/org/onosproject/ui/table/CellComparator.java b/core/api/src/main/java/org/onosproject/ui/table/CellComparator.java
index 55c84c8..bb6b185 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/CellComparator.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/CellComparator.java
@@ -24,21 +24,19 @@
     /**
      * 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 nulls are permitted, and should be sorted to the beginning
      * of an ascending sort; i.e. null is considered to be "smaller" than
      * non-null values.
      *
      * @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
      */
     int compare(Object o1, Object o2);
 
diff --git a/core/api/src/main/java/org/onosproject/ui/table/TableModel.java b/core/api/src/main/java/org/onosproject/ui/table/TableModel.java
index ed5db2e..9ec2e3b 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/TableModel.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/TableModel.java
@@ -50,6 +50,8 @@
  */
 public class TableModel {
 
+    private static final String DESC = "desc";
+
     private static final CellComparator DEF_CMP = DefaultCellComparator.INSTANCE;
     private static final CellFormatter DEF_FMT = DefaultCellFormatter.INSTANCE;
     private static final String EMPTY = "";
@@ -220,6 +222,9 @@
         Collections.sort(rows, new RowComparator(id1, dir1, id2, dir2));
     }
 
+    private boolean nullOrEmpty(String s) {
+        return s == null || EMPTY.equals(s.trim());
+    }
 
     /** Designates sorting direction. */
     public enum SortDir {
@@ -229,9 +234,6 @@
         DESC
     }
 
-    private boolean nullOrEmpty(String s) {
-        return s == null || EMPTY.equals(s.trim());
-    }
 
     /**
      * Row comparator.
@@ -381,8 +383,6 @@
         }
     }
 
-    private static final String DESC = "desc";
-
     /**
      * Returns the appropriate sort direction for the given string.
      * <p>
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 {
 
diff --git a/incubator/api/src/main/java/org/onosproject/incubator/net/tunnel/TunnelEndPointFormatter.java b/incubator/api/src/main/java/org/onosproject/incubator/net/tunnel/TunnelEndPointFormatter.java
index 5414f2c..cc68876 100644
--- a/incubator/api/src/main/java/org/onosproject/incubator/net/tunnel/TunnelEndPointFormatter.java
+++ b/incubator/api/src/main/java/org/onosproject/incubator/net/tunnel/TunnelEndPointFormatter.java
@@ -20,9 +20,11 @@
 import org.onosproject.ui.table.CellFormatter;
 import org.onosproject.ui.table.cell.AbstractCellFormatter;
 
+import java.util.Optional;
+
 /**
- * Formats a optical tunnel endpoint as "(type)/(element-id)/(port)".
- * Formats a ip tunnel endpoint as "ip".
+ * Formats an optical tunnel endpoint as "(type)/(element-id)/(port)".
+ * Formats an IP tunnel endpoint as "ip".
  */
 @Beta
 public final class TunnelEndPointFormatter extends AbstractCellFormatter {
@@ -30,17 +32,26 @@
     private TunnelEndPointFormatter() {
     }
 
+    private String safeOptional(Optional<?> optional) {
+        return optional.isPresent() ? optional.get().toString() : QUERY;
+    }
+
     @Override
     protected String nonNullFormat(Object value) {
 
         if (value instanceof DefaultOpticalTunnelEndPoint) {
-            DefaultOpticalTunnelEndPoint cp = (DefaultOpticalTunnelEndPoint) value;
-            return cp.type() + "/" + cp.elementId().get() + "/" + cp.portNumber().get();
+            DefaultOpticalTunnelEndPoint ep =
+                    (DefaultOpticalTunnelEndPoint) value;
+
+            String e = safeOptional(ep.elementId());
+            String p = safeOptional(ep.portNumber());
+            return ep.type() + SLASH + e + SLASH + p;
+
         } else if (value instanceof IpTunnelEndPoint) {
             IpTunnelEndPoint cp = (IpTunnelEndPoint) value;
             return cp.ip().toString();
         }
-        return "";
+        return EMPTY;
     }
 
     /**