String sql="select * from userpassword where username=? and password=?";
    pst = (OraclePreparedStatement) con.prepareStatement(sql);
    pst.setString(1,text_username.getText());
    pst.setString(2,pass_password.getText());
    rs = (OracleResultSet) pst.executeQuery();
    if(rs.next()){

         text_username.setText("");
         pass_password.setText("");
         ModulesForm Mo = new ModulesForm();
         Mo.setVisible(true);
    }
    else{
        JOptionPane.showMessageDialog(null, "enter valid username and id !!!");
    }
    con.close();
}catch(Exception e){
    JOptionPane.showMessageDialog(null, "some error occured. try again later !!!");
}