private void btnPresentarActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_btnPresentarActionPerformed
        // TODO add your handling code here:
        JFrame d = new JFrame("LIBRETA");
        JPanel agenda = new LibretaCalificaciones();
        d.setContentPane(agenda);
        Dimension de = Toolkit.getDefaultToolkit().getScreenSize();
        d.setBounds((de.width - 940) / 2, (de.height - 715) / 2, 940, 715);
        d.pack();
        d.setVisible(true);

    }//GEN-LAST:event_btnPresentarActionPerformed