Java key listener in Commandline

Swing is different from a command line environment in the sense that you have no events in a console window. A standard GUI deals with objects and events. A console has no such equivalent notion.

What you do have is a standard input (as well as a standard output), which you can read from. See this question on how to read a single char from console (without waiting for a newline) - or rather, on how this isn't very easy to do in Java.

Of course, you can always do the reading asynchronously on a separate thread. i.e. the main thread will keep doing stuff, with a listener thread waiting on the I/O blocking call. But this can only be implemented and handled on the application level.

you can use BufferedReader in a loop:

BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String line = "";

   while (line.equalsIgnoreCase("quit") == false) {
       line = in.readLine();

       //do something
   }

   in.close();