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    <p>You need to learn to walk before you start trying to run.</p> <ul> <li><p>Read / do a tutorial on Java programming. This should explain (among other things) how to compile and run a Java program from the command line.</p></li> <li><p>Read / do a tutorial on JMS.</p></li> <li><p>Read the Oracle material on how to create an executable JAR file.</p></li> <li><p>Figure out what it is you are trying to do ... and <strong>design</strong> your application.</p></li> </ul> <hr> <p>Looking at what you've shown and told us:</p> <ul> <li><p>You <em>could</em> add a main method to that class, but to make an <em>executable</em> JAR file, you've got to create your JAR file with a manifest entry that specifies the name of the class with the main method.</p></li> <li><p>There's a lot more that you have to do before that code will work:</p> <ul> <li><p>add code to (at least) log the exceptions that you are catching</p></li> <li><p>add code to process the messages</p></li> <li><p>add code to initialize the connection factory and connection objects</p></li> </ul></li> <li><p>And like I said above, you probably need some kind of design ... so that you don't end up with everything in a "kitchen sink" class.</p></li> </ul> <hr> <blockquote> <p>if I add main method, should I simply call receiveMessages() in main? </p> </blockquote> <p>That is one approach. But like I said, you really need to <em>design</em> your application.</p> <blockquote> <p>And then after running, will the listener keep on running? </p> </blockquote> <p>It is not entirely clear. It should keep running as long as the <code>main</code> thread is alive, but it is not immediately obvious what happens when your <code>main</code> method returns. (It depends on whether the JMS threads are created as daemon threads, and that's not specified.)</p> <blockquote> <p>And if there are messages, will it retrieve automatically in onMessage method? </p> </blockquote> <p>It would appear that each message is retrieved (read from the socket) <em>before</em> your <code>onMessage</code> method is called.</p> <hr> <blockquote> <p>Also, if the listener is continuously listening, doesn't it take CPU???</p> </blockquote> <p>Not if it is implemented properly.</p> <blockquote> <p>In case of threads, when we create a thread &amp; put it in sleep, the CPU utilization is zero, how doe it work in case of listener?</p> </blockquote> <p>At a certain level, a listener thread will make a system call that <em>waits</em> for data to arrive on a network socket. I don't know how it is exactly implemented, but this <em>could</em> be as simple as an <code>read()</code> call on the network socket's <code>InoutStream</code>. No CPU is used by a thread while it waits in a blocking system call.</p>
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    1. COif I add main method, should I simply call receiveMessages() in main? And then after running, will the listener keep on running? And if there are messages, will it retrieve automatically in onMessage method?
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