Enable checkstyle rule that looks for final classes.

Enabled the checkstyle rule that checks if classes that could
be final are made final, and fixed the violations that were
reported.

Change-Id: I07ca27f420855116959c1bef3648330cd266ddd8
diff --git a/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java b/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java
index be9fce5..b5c1ae7 100644
--- a/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java
+++ b/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java
@@ -4,7 +4,7 @@
 import net.onrc.onos.core.datastore.ramcloud.RCClient;
 
 // This class probably need to be a service
-public class DataStoreClient {
+public final class DataStoreClient {
     private static final String BACKEND = System.getProperty("net.onrc.onos.core.datastore.backend", "hazelcast");
 
     // Suppresses default constructor, ensuring non-instantiability.
diff --git a/src/main/java/net/onrc/onos/core/datastore/hazelcast/HZClient.java b/src/main/java/net/onrc/onos/core/datastore/hazelcast/HZClient.java
index 4cc68b4..32ff15b 100644
--- a/src/main/java/net/onrc/onos/core/datastore/hazelcast/HZClient.java
+++ b/src/main/java/net/onrc/onos/core/datastore/hazelcast/HZClient.java
@@ -30,7 +30,7 @@
 import com.hazelcast.core.HazelcastInstance;
 import com.hazelcast.core.IMap;
 
-public class HZClient implements IKVClient {
+public final class HZClient implements IKVClient {
     private static final Logger log = LoggerFactory.getLogger(HZClient.class);
 
     static final long VERSION_NONEXISTENT = 0L;
diff --git a/src/main/java/net/onrc/onos/core/datastore/utils/ByteArrayUtil.java b/src/main/java/net/onrc/onos/core/datastore/utils/ByteArrayUtil.java
index 32abb59..96d0048 100644
--- a/src/main/java/net/onrc/onos/core/datastore/utils/ByteArrayUtil.java
+++ b/src/main/java/net/onrc/onos/core/datastore/utils/ByteArrayUtil.java
@@ -2,7 +2,7 @@
 
 import java.nio.ByteBuffer;
 
-public class ByteArrayUtil {
+public final class ByteArrayUtil {
 
     // Suppresses default constructor, ensuring non-instantiability.
     private ByteArrayUtil() {
diff --git a/src/main/java/net/onrc/onos/core/flowprogrammer/FlowPusher.java b/src/main/java/net/onrc/onos/core/flowprogrammer/FlowPusher.java
index b9b093f..3f5326e 100644
--- a/src/main/java/net/onrc/onos/core/flowprogrammer/FlowPusher.java
+++ b/src/main/java/net/onrc/onos/core/flowprogrammer/FlowPusher.java
@@ -82,7 +82,7 @@
  *
  * @author Naoki Shiota
  */
-public class FlowPusher implements IFlowPusherService, IOFMessageListener {
+public final class FlowPusher implements IFlowPusherService, IOFMessageListener {
     private static final Logger log = LoggerFactory.getLogger(FlowPusher.class);
     protected static final int DEFAULT_NUMBER_THREAD = 1;
 
@@ -239,7 +239,7 @@
      *
      * @author Naoki
      */
-    private static class BarrierInfo {
+    private static final class BarrierInfo {
         final long dpid;
         final int xid;