title: JPanel doesn't response to KeyListener event
body: <p>I have a subclass of <code>JFrame</code> that uses a class extended from <code>JPanel</code></p>
  
  <pre><code>public class HelloWorld extends JPanel implements KeyListener
  </code></pre>
  
  <p>I add an object of <code>HelloWorld</code> to the frame - <code>app.add(helloWorld);</code>. Now, when I press any keyboard key non of the <code>KeyListener</code> methods gets called and it seems that <code>helloWorld</code> doesn't have window focus. I have tried also to invoke <code>helloWorld.requestFocusInWindow();</code> but still doesn't respond.</p>
  
  <p>How can I make it respond to key press?</p>