在另一个JComboBox中选择一个项目时如何显示JComboBox

Question

I'm trying to display values in JComboBox B when I select items from JComboBox A . So far, nothing happened when I select a value from JComboBox A . Here is my data and code. So for instance, if I select 1 from my JComboBox A (paperid), my result in JComboBox B (authorid) will be 1,2,4.

JComboBox A

JComboBox B

private void comboboxAPopupMenuWillBecomeInvisible(javax.swing.event.PopupMenuEvent evt) { 

    String display = (String) comboboxA.getSelectedItem();
    String sql = "Select authorid from submission where paperid =?";

    try {
        ps=conn.prepareStatement(sql);
        ps.setString(1,display);
        rset = ps.executeQuery();

        if (rset.next()){
               String add1 = rset.getString("authorid");
               System.out.println(add1);
               comboboxB.setSelectedItem(add1);
        }

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

Answer 1

I think that I've understood your question at last. You want the result of the query to be charged in the second combobox, don't you?

If that's the case, try this

 private void comboboxAPopupMenuWillBecomeInvisible(javax.swing.event.PopupMenuEvent evt) { 

    String display = (String) comboboxA.getSelectedItem();
    String sql = "Select authorid from submission where paperid =?";

    comboboxB.removeAllItems(); // <- Clear comboboxB

    try {
        ps = conn.prepareStatement(sql);
        ps.setString(1, display);
        rset = ps.executeQuery();

        while (rset.next()) {  // <- Include all authors found
           String add1 = rset.getString("authorid");
           System.out.println(add1);
           comboboxB.addItem(add1);
        }

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

Maybe you have to force a repaint in the container where the JComboBoxes are displayed after the execution of this method. "myContainer" is not the variable name, replace with the name of your panel or your frame.

   myContainer.revalidate(); 
   myContainer.repaint();