Hi Sameer,

I confirm you that Lightstreamer is a perfectly suited solution for the scenario of a quiz contest.

You can look at the Simple Chat Demo or at the Basic Instant Messenger Demo for examples of bi-directional comunication from server to clients and from clients to server.
They are both based on a Java Adapter and can be considered a reference example of, respectively: messages broadcast and one-to-one messaging.

Furthermore, here you can find a modified HelloWorldDataAdapter that polls a mySql db.