Make the factories final

src/factory/CommandFactory.java

@@ -7,7 +7,7 @@ import server.SendToReplica;
 import java.io.OutputStream;
 import java.util.List;
 
-public class CommandFactory implements Factory {
+public final class CommandFactory implements Factory {
 
     private static final class FactoryHolder {
         private static final CommandFactory factory = new CommandFactory();

src/factory/replica/ReplicaCommandFactory.java

@@ -9,7 +9,7 @@ import model.Command;
 
 import java.util.List;
 
-public class ReplicaCommandFactory implements Factory {
+public final class ReplicaCommandFactory implements Factory {
     private static final class ReplicaFactoryHolder {
         private static final ReplicaCommandFactory factory = new ReplicaCommandFactory();
     }