How do I restrict the number of characters to be entered in a TextField?
Setting a maximum character count is not a built-in function of
TextField. You have to subclass TextField to implement this yourself.
You want to intercept the keystrokes before they are recorded and
count how many characters have been added, accounting for backspace.
If the number of characters entered so far is less than the
maximum, allow the KEY_TYPED KeyEvent to be processed; otherwise
ignore the event.