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/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() {