title: java zkoss EventListener how to get variables of event
body: <p>I debug from EventListener in InteliJ IDEA and get some variables like _val, _oldVal, _selbk, _start, _name ... But I don't know how to get those variables.
  Here is my code:</p>
  
  <pre><code>myDoublebox.addEventListener(Events.ON_CHANGE, new org.zkoss.zk.ui.event.EventListener() {
      @Override
      public void onEvent(Event event) throws Exception {
          //just for debug
          System.out.println(event);
      }
  });
  </code></pre>