与SQL的java连接（java.lang…）

Question

我的java代码有一个很大的问题

这是我的“代码在运行”按钮上的侦听器

例外情况是：

in output writen(java.lang.nullpointerexception)

谢谢你的帮助

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {

    // # declaration

    String naw_syani=naw.getText();
    String zhmara_f=zhmara_form.getText().trim();
    String zhmara_nas=zhmara_nasnama.getText().trim();
    String zhmara_mob=zhmara_mobile.getText().trim();
    String zhmara_mob2=zhmara_mobile2.getText().trim();
    String zhmara_mall=zhmara_xanw.getText().trim();
    String barwar=jDateChooser2.getDateFormatString();

    // # connection

    PreparedStatement stat;
    ResultSet rs;

    String sql ="insert into xallk values ('"+"', 'mitan', 'moran', 'mimie', 245,235);";
    try 
    {
       stat = (PreparedStatement) conn.prepareCall(sql);
       stat.execute();
       System.out.println("chw");
    }
    catch (SQLException e) 
    {
         System.out.println("insert nabw!"+e);
    }

}