显示jcombobox的金额

Question

我在mysql中有一个非常简单的表，我能够将表中的所有名称显示在组合框中，但我想在字段上显示等效数量。似乎没有运行时错误，但没有任何反应，请帮助。

我在点击添加项目时添加了该方法。以下是我添加项目的代码以及从组合框中获取金额的方法。

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

    try {

   String sql = "Insert into item (NAME,AMOUNT) values (?,?)";

   pst = con.prepareStatement(sql);
   String value  = INSERTdrp.getSelectedItem().toString();
   pst.setString(1,value);

   pst.setString(2, AMOUNTfld.getText());

   pst.execute();





} catch (SQLException ex ) {
    System.out.println("error connecting" + ex );
    JOptionPane.showMessageDialog(null,"Query Failed");





 }
        AMOUNTfld.setText("");

    updateCombo();
      amountPull();
      update_Table();

提取金额

         private void amountPull() {

         try {


        String query  = "select * from item";
        st = con.prepareStatement(query);


        String value  = INSERTdrp.getSelectedItem().toString();
       pst.setString(1,value);


    rs = st.executeQuery(query);

        while(rs.next()) {
       String amount = rs.getString("AMOUNT"); 
        amountDisplay.setText(amount);

        }

    } catch(SQLException ex) {

         JOptionPane.showMessageDialog(null,ex);
    }}

以下是我的代码的另一部分

    private void fillCombo() {

     try {


        String query  = "select * from item";
        st = con.prepareStatement(query);
        rs = st.executeQuery(query);


        while(rs.next()) {
       String name = rs.getString("NAME"); 
        INSERTdrp.addItem(name);

        }

    } catch(Exception ex) {

    }}

   private void updateCombo() {

        INSERTdrp.removeAllItems();


       try {


        String query  = "select * from item";
        st = con.prepareStatement(query);
        rs = st.executeQuery(query);


        while(rs.next()) {
       String name = rs.getString("NAME"); 
        INSERTdrp.addItem(name);

        }

    } catch(SQLException ex) {

        JOptionPane.showMessageDialog(null,ex);

    } 

    }



       private void update_Table() {

       try {

        String query  = "select * from item";
        st = con.prepareStatement(query);
        rs = st.executeQuery(query);
        tableList.setModel(DbUtils.resultSetToTableModel(rs));




    } catch(SQLException ex) {

         JOptionPane.showMessageDialog(null,ex);

    } 


   }