PreparedStatement stl = null;
 ResultSet rs = null;
 Connection con = null;



public NovoJFrame() {
    initComponents();

    IniciarBD();

    this.PrencherComboBox();

    jPanel3.setVisible(false);
}


public void PrencherComboBox(){
    String sql = "Select *from ALUNO";
    try {

           stl = con.prepareStatement(sql);
           rs = stl.executeQuery();

           while(rs.next()){
               jComboBox1.addItem(rs.getString("NOME"));
           }
       } catch(SQLException ex){
           JOptionPane.showMessageDialog(null,ex);
       }

}