addKeyListener is NOT working

When I press a key the keyPressed() procedure is NOT called. Why ?
In contrast the button events working successfully.

Possible the key-Event is not forwarded to the "outer" level.
How do I forward these events otherwise?

public class xxx extends JFrame implements ActionListener, KeyListener {
      boolean inAnApplet = true;

      public xxx() {
      
         ...
         mybutton.addActionListener(this);
         ...
         addKeyListener(this);
         ...
         ...
         addWindowListener(new WindowAdapter() {
               public void windowClosing(WindowEvent e) {
                   if (inAnApplet) {
                       dispose();
                   } else {
                       System.exit(0);
                   }
               }
           });
          }
          
      public void keyPressed(KeyEvent e) {
     System.out.println("In KeyPressed"); // never reached !!
     ... }
    
     public void actionPerformed(ActionEvent e){
        System.out.println("In ActPerf"); //reached !!
        ... }
      }

   public static void main(String args[]) {
      ...
      xxx window = new xxx();
      }

Lars