diff --git a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/TenantNetworkWebResource.java b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/TenantNetworkWebResource.java
index 026a8ac..200ce09 100644
--- a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/TenantNetworkWebResource.java
+++ b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/TenantNetworkWebResource.java
@@ -123,13 +123,13 @@
     }
 
     private State isState(String state) {
-        if (state.equals("ACTIVE")) {
+        if ("ACTIVE".equals(state)) {
             return TenantNetwork.State.ACTIVE;
-        } else if (state.equals("BUILD")) {
+        } else if ("BUILD".equals(state)) {
             return TenantNetwork.State.BUILD;
-        } else if (state.equals("DOWN")) {
+        } else if ("DOWN".equals(state)) {
             return TenantNetwork.State.DOWN;
-        } else if (state.equals("ERROR")) {
+        } else if ("ERROR".equals(state)) {
             return TenantNetwork.State.ERROR;
         } else {
             return null;
@@ -137,7 +137,7 @@
     }
 
     private Type isType(String type) {
-        if (type.equals("LOCAL")) {
+        if ("LOCAL".equals(type)) {
             return TenantNetwork.Type.LOCAL;
         } else {
             return null;
@@ -286,7 +286,7 @@
         String segmentationIdStr = node.get("provider:segmentation_id").asText();
         SegmentationId segmentationId = SegmentationId.segmentationId(segmentationIdStr);
         TenantId tenantId = TenantId.tenantId(tenantIdStr);
-        if (segmentationIdStr == null || segmentationIdStr.equals("null")) {
+        if (segmentationIdStr == null || "null".equals(segmentationIdStr)) {
             segmentationId = get(VtnRscService.class).getL3vni(tenantId);
         }
         TenantNetworkId id = null;
@@ -337,7 +337,7 @@
             String segmentationIdStr = node.get("provider:segmentation_id").asText();
             SegmentationId segmentationId = SegmentationId.segmentationId(segmentationIdStr);
             TenantId tenantId = TenantId.tenantId(tenantIdStr);
-            if (segmentationIdStr == null || segmentationIdStr.equals("null")) {
+            if (segmentationIdStr == null || "null".equals(segmentationIdStr)) {
                 segmentationId = get(VtnRscService.class).getL3vni(tenantId);
             }
             network = new DefaultTenantNetwork(
diff --git a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/VirtualPortWebResource.java b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/VirtualPortWebResource.java
index 1e1cc79..af82f9b 100644
--- a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/VirtualPortWebResource.java
+++ b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/resources/VirtualPortWebResource.java
@@ -387,7 +387,7 @@
      * @return the virtualPort state
      */
     private State isState(String state) {
-        if (state.equals("ACTIVE")) {
+        if ("ACTIVE".equals(state)) {
             return VirtualPort.State.ACTIVE;
         } else {
             return VirtualPort.State.DOWN;
diff --git a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FloatingIpCodec.java b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FloatingIpCodec.java
index cd61280..05cfaae 100644
--- a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FloatingIpCodec.java
+++ b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FloatingIpCodec.java
@@ -60,36 +60,36 @@
         Iterator<String> i = fields.iterator();
         while (i.hasNext()) {
             String s = i.next();
-            if (s.equals("floating_network_id")) {
+            if ("floating_network_id".equals(s)) {
                 result.put("floating_network_id", floatingIp.networkId()
                         .toString());
             }
-            if (s.equals("router_id")) {
+            if ("router_id".equals(s)) {
                 result.put("router_id",
                            floatingIp.routerId() == null ? null : floatingIp
                                    .routerId().routerId());
             }
-            if (s.equals("tenant_id")) {
+            if ("tenant_id".equals(s)) {
                 result.put("tenant_id", floatingIp.tenantId().toString());
             }
-            if (s.equals("port_id")) {
+            if ("port_id".equals(s)) {
                 result.put("port_id",
                            floatingIp.portId() == null ? null : floatingIp
                                    .portId().toString());
             }
-            if (s.equals("id")) {
+            if ("id".equals(s)) {
                 result.put("id", floatingIp.id().floatingIpId().toString());
             }
-            if (s.equals("fixed_ip_address")) {
+            if ("fixed_ip_address".equals(s)) {
                 result.put("fixed_ip_address",
                            floatingIp.fixedIp() == null ? null : floatingIp
                                    .fixedIp().toString());
             }
-            if (s.equals("floating_ip_address")) {
+            if ("floating_ip_address".equals(s)) {
                 result.put("floating_ip_address", floatingIp.floatingIp()
                         .toString());
             }
-            if (s.equals("status")) {
+            if ("status".equals(s)) {
                 result.put("status", floatingIp.status().toString());
             }
         }
diff --git a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FlowClassifierCodec.java b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FlowClassifierCodec.java
index e4d4b93..c760c9c 100644
--- a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FlowClassifierCodec.java
+++ b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/FlowClassifierCodec.java
@@ -75,12 +75,12 @@
         String etherType = nullIsIllegal(json.get(ETHER_TYPE), ETHER_TYPE + MISSING_MEMBER_MESSAGE).asText();
         resultBuilder.setEtherType(etherType);
 
-        if (json.get(PROTOCOL) != null && !(json.get(PROTOCOL)).asText().equals("null")) {
+        if (json.get(PROTOCOL) != null && !"null".equals((json.get(PROTOCOL)).asText())) {
             String protocol = (json.get(PROTOCOL)).asText();
             resultBuilder.setProtocol(protocol);
         }
 
-        if (json.get(PRIORITY) != null && !(json.get(PRIORITY)).asText().equals("null")) {
+        if (json.get(PRIORITY) != null && !"null".equals((json.get(PRIORITY)).asText())) {
             int priority = (json.get(PRIORITY)).asInt();
             resultBuilder.setPriority(priority);
         }
@@ -97,22 +97,22 @@
         int maxDstPortRange = (json.get(MAX_DST_PORT_RANGE)).asInt();
         resultBuilder.setMaxDstPortRange(maxDstPortRange);
 
-        if (json.get(SRC_IP_PREFIX) != null && !(json.get(SRC_IP_PREFIX)).asText().equals("null")) {
+        if (json.get(SRC_IP_PREFIX) != null && !"null".equals((json.get(SRC_IP_PREFIX)).asText())) {
             String srcIpPrefix = (json.get(SRC_IP_PREFIX)).asText();
             resultBuilder.setSrcIpPrefix(IpPrefix.valueOf(srcIpPrefix));
         }
 
-        if (json.get(DST_IP_PREFIX) != null && !(json.get(DST_IP_PREFIX)).asText().equals("null")) {
+        if (json.get(DST_IP_PREFIX) != null && !"null".equals((json.get(DST_IP_PREFIX)).asText())) {
             String dstIpPrefix = (json.get(DST_IP_PREFIX)).asText();
             resultBuilder.setDstIpPrefix(IpPrefix.valueOf(dstIpPrefix));
         }
 
-        if (json.get(SRC_PORT) != null && !(json.get(SRC_PORT)).asText().equals("null")) {
+        if (json.get(SRC_PORT) != null && !"null".equals((json.get(SRC_PORT)).asText())) {
             String srcPort = (json.get(SRC_PORT)).asText();
             resultBuilder.setSrcPort(VirtualPortId.portId(srcPort));
         }
 
-        if (json.get(DST_PORT) != null && !(json.get(DST_PORT)).asText().equals("null")) {
+        if (json.get(DST_PORT) != null && !"null".equals((json.get(DST_PORT)).asText())) {
             String dstPort = (json.get(DST_PORT)).asText();
             resultBuilder.setDstPort(VirtualPortId.portId(dstPort));
         }
diff --git a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/RouterCodec.java b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/RouterCodec.java
index b6819b2..b602108 100644
--- a/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/RouterCodec.java
+++ b/apps/vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/RouterCodec.java
@@ -59,26 +59,26 @@
         Iterator<String> i = fields.iterator();
         while (i.hasNext()) {
             String s = i.next();
-            if (s.equals("id")) {
+            if ("id".equals(s)) {
                 result.put("id", router.id().routerId());
             }
-            if (s.equals("status")) {
+            if ("status".equals(s)) {
                 result.put("status", router.status().toString());
             }
-            if (s.equals("name")) {
+            if ("name".equals(s)) {
                 result.put("name", router.name().toString());
             }
-            if (s.equals("admin_state_up")) {
+            if ("admin_state_up".equals(s)) {
                 result.put("admin_state_up", router.adminStateUp());
             }
-            if (s.equals("tenant_id")) {
+            if ("tenant_id".equals(s)) {
                 result.put("tenant_id", router.tenantId().toString());
             }
-            if (s.equals("routes")) {
+            if ("routes".equals(s)) {
                 result.put("routes", router.routes() == null ? null : router
                         .routes().toString());
             }
-            if (s.equals("external_gateway_info")) {
+            if ("external_gateway_info".equals(s)) {
                 result.set("external_gateway_info",
                            router.externalGatewayInfo() == null ? null
                                                                : new RouterGatewayInfoCodec()