diff --git a/core/common/src/main/java/alluxio/collections/ConcurrentHashSet.java b/core/common/src/main/java/alluxio/collections/ConcurrentHashSet.java
index <HASH>..<HASH> 100644
--- a/core/common/src/main/java/alluxio/collections/ConcurrentHashSet.java
+++ b/core/common/src/main/java/alluxio/collections/ConcurrentHashSet.java
@@ -28,7 +28,7 @@ import javax.annotation.concurrent.ThreadSafe;
  * @param <T> the type of the set objects
  */
 @ThreadSafe
-public class ConcurrentHashSet<T> extends AbstractSet<T> {
+public final class ConcurrentHashSet<T> extends AbstractSet<T> {
   // COMPATIBILITY: This field needs to declared as Map (as opposed to ConcurrentHashMap). The
   // reason is that the return type of ConcurrentHashMapV8#keySet() has changed from Set<K> to
   // KeySetView<K,V> between Java 7 and Java 8 and this can result in a NoSuchMethod runtime
@@ -134,7 +134,7 @@ public class ConcurrentHashSet<T> extends AbstractSet<T> {
 
   @Override
   public Object[] toArray() {
-    return mMap.keySet().toArray();
+    return mMap.keySet().toArray(); ConcurrentHashSet.java
   }
 
   @Override
add final to concurrenthashset.java