求教keylistener的问题

[Jhomson]

本人菜鸟，在看《java大学简明教程》的教程22时碰到一个很困惑的问题，代码我都贴出来了（原书上的代码，并未修改），就是关于为什么每次按下键盘后，outputJTextArea中的内容就会变化，代码中好像没有有关outputJTextArea更新的语句，求高手指点迷津！！！

 outputJTextArea.addKeyListener(

         new KeyListener() // anonymous inner class
         {
            // event handler called when any key is pressed
            public void keyPressed( KeyEvent event )
            {
               outputJTextAreaKeyPressed( event );
            }

            // event handler called when any key is released
            public void keyReleased( KeyEvent event )
            {
               outputJTextAreaKeyReleased( event );
            }

            // event handler called when any key is typed
            public void keyTyped( KeyEvent event )
            {
            }

         } // end anonymous inner class

      ); // end call to addKeyListener

      outputJTextArea.addFocusListener(

         new FocusAdapter() // anonymous inner class
         {
            // event handler called when outputJTextArea loses focus
            public void focusLost( FocusEvent event )
            {
               outputJTextAreaFocusLost( event );
            }

         } // end anonymous inner class

      ); // end call to addFocusListener

[调皮的芋头]

看下 outputJTextAreaKeyPressed( event ) 方法的具体实现