No more than 4 characters and the first char will be C

Question

with this method
public void keyTyped(KeyEvent e) {
          if (e.getSource() == txtCode ) {
               char c = e.getKeyChar();
               if (!((Character.isDigit(c) || (c == KeyEvent.VK_BACK_SPACE)
                         || (c == '.') || (c == KeyEvent.VK_DELETE)))) {
                    getToolkit().beep();
                    e.consume();
          }

Answer 1

My standard answer (which is darn handy since there is no proper question)
is that this code is wrong. How do I know? How does BDLH do it? It's
actually quite simple, there's really nothing to it! A KeyListener is an awkward
and error-prone approach to almost any problem involving text components.
Instead, check out (depending on your problem):
DocumentFilter:
http://java.sun.com/javase/6/docs/api/javax/swing/text/DocumentFilter.html
A custom document:
http://java.sun.com/javase/6/docs/api/javax/swing/text/Document.html
In particular, check out the sample code at the start of the documentation
for JTextField:
http://java.sun.com/javase/6/docs/api/javax/swing/JTextField.html
Be sure to study the tutorial as well:
http://java.sun.com/docs/books/tutorial/uiswing/components/text.html