The TopicSubscriber receives messages from the message server one at a time (serially).
These messages are pushed from the message server to the TopicSubscriber asynchronously, which means that the TopicSubscriber does not have to poll the message
server for messages. In our example, each chat client will receive any message published
by any of the other chat clients. When a user enters text at the command line, the text
message is delivered to all other chat clients that subscribe to the same topic.
How does a network client get a message from the JMS server asynchronously without polling the server?
What do they mean by it? Please explain....