Intenta con:
tfPantalla.addKeyListener(new KeyAdapter(){
public void keyPressed(KeyEvent e){
tfPantalla.setText(e.getKeyChar());
}
});public char getKeyChar()
Returns the character associated with the key in this event. For example, the key-typed event for shift + "a" returns the value for "A".
Returns:
the Unicode character defined for this key event. If no valid Unicode character exists for this key event, keyChar is CHAR_UNDEFINED.
Saludos.