public void SoloLetras(JTextField a) {
        a.addKeyListener(new KeyAdapter() {
            public void keyTyped(KeyEvent e) {
                char c = e.getKeyChar();
                if (!Character.isAlphabetic(c) && !Character.isLetter(c)) {
                    getToolkit().beep();
                    e.consume();
                }
            }
        });
    }