They can't get keycode value other than signs of ascii on the keyboard.
There are a lot of types of keyboard. But most of keys aren't supported
in Java. So program can't get those key code when the key is pressed.

For example, they useally use japanese keyboard in Japan. And the keyboard
has Japanese kana signs on the key tops. The program can get its key code
without software input method on the platform. But on Java those don't work.