java - 无法从 SQL 表获取我的数据

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请看一下这段代码，让我知道哪里出了问题。我的 JDBC 已连接，但单击“确定”按钮时仍然未显示数据。

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

        DefaultTableModel dtm=(DefaultTableModel)t1.getModel();
        try
        {
             st=con.createStatement();
            sql="Select * from train";
            rs=st.executeQuery(sql);

            if (rs.next())
            {
                  tn = rs.getInt("TrainNo");
                tna = rs.getString("Train_Name");
                s = rs.getString("Start");
                d = rs.getDate("Departure");
                stp = rs.getString("Stop");
                a = rs.getDate("Arrival");
                da = rs.getString("Days");
                c = rs.getString("Class");
               Object []obj={tn,tna,s,d,stp,a,da,c};
            dtm.addRow(obj);

            }
        }
        catch(Exception ex)
        {
            JOptionPane.showMessageDialog(null, ex.getMessage());
        }
    }

Answer 1

可能您忘记添加标题。所以它可能看起来像这样:

    String[] header = {"TrainNo","Train Name","Start","Departure","Stop","Arrival","Days","Class"};
    DefaultTableModel dtm = new DefaultTableModel(null,header);
    try {
       st=con.createStatement();
       sql="Select * from train";
       rs=st.executeQuery(sql);
       while ( rs.next() ) {
         tn = rs.getInt("TrainNo");
         tna = rs.getString("Train_Name");
         s = rs.getString("Start");
         d = rs.getDate("Departure");
         stp = rs.getString("Stop");
         a = rs.getDate("Arrival");
         da = rs.getString("Days");
         c = rs.getString("Class");
        Object []obj={tn,tna,s,d,stp,a,da,c};
        dtm.addRow(obj);
      }  
      st.close();
      rs.close();       
    }
    catch(Exception ex)
    {
       JOptionPane.showMessageDialog(null, ex.getMessage());
    }
    t1 = new JTable(dtm);