//First implement KeyLisnter in ur class.
//then add keyListner to ur textField as
txtBet.addKeyListener(this);
 
//now implement all the methods of keyListner. in the class.
 
public void keyPressed(KeyEvent e)
{
 
 int i = e.getKeyCode();
  if(i=1 || i=2....)//check
 {
  //Kick the user.
 } 
//or u can do it other way
 
 try
{
intBet = Integer.parseInt( txtBet.getText() );
}
catch (NumberFormatException e)
{
message = "The bet you entered is not a legal
number!";
}
public void keyTyped(KeyEvent e) {}
public void keyReleased(KeyEvent e) {}