Have you checked Sun's Java API documentation? You can do what you want by using the
Robot class to simulate input. It does come with some caveats, but it should get you started. Note that you'll need to simulate press and release events. For the virtual key codes used in Java, see the
KeyEvent class.
If all you want to do is map lowercase letters to their uppercase counterparts, you can use a lookup table,
switch() block, or the Java API methods to accomplish this (things like
String.toUpperCase() and similar methods).