What is the difference between a MessageListener and a Consumer in JMS?

Question

I am new to JMS. As far as I understood Consumers are capable of picking messages from queue/topic. So why do you need a MessageList

Answer 1

The difference is that MessageConsumer is used to receive messages synchronously:

MessageConsumer mc = s.createConsumer(queue);
Message msg = mc.receive();

For asynchronous delivery, we can register a MessageListener object with a message consumer:

mc.setMessageListener(new MessageListener() {
    public void onMessage(Message msg) {
        ...
    }
});