使用ComboBox填充ComboBox

Question

我这里有一个问题，combobox2中的项目不是被替换，而是堆栈。我试图将bookss.removeAllItems()；放在bookss.addItem(Names)之上；但每当我单击combobox1中的其他项时，都会得到一个错误。

这是我的代码

String caa = categorys.getSelectedItem().toString();
if ("Fiction".equals(caa))
{
    String acct = categorys.getSelectedItem().toString();
    try{
        pst = con.prepareStatement("select * from books where category=?");
        pst.setString(1, acct);
        ResultSet rsf = pst.executeQuery();
        rsf.next();
        try{
            rsf = stmt.executeQuery("select * from BOOKS WHERE category='Fiction'");
            while(rsf.next())
            {
                String names = rsf.getString("book_title");
                bookss.addItem(names);
            }
            }catch(SQLException err){
            System.out.println(err);
        }
        }catch(SQLException e){
        JOptionPane.showMessageDialog(null, e);
    }
}
if ("Horror".equals(caa))
{
    String acct = categorys.getSelectedItem().toString();
    try{
        pst = con.prepareStatement("select * from books where category=?");
        pst.setString(1, acct);
        ResultSet tts = pst.executeQuery();
        tts.next();
        try{
            tts = stmt.executeQuery("select * from BOOKS WHERE category='Horror'");
            while(tts.next())
            {
                String names = tts.getString("book_title");
                bookss.addItem(names);
            }
            }catch(SQLException err){
            System.out.println(err);
        }
        }catch(SQLException e){
        JOptionPane.showMessageDialog(null, e);
    }
}

Answer 1

使用以下命令：

DefaultComboBoxModel model = (DefaultComboBoxModel) ComboBox.getModel();
model.removeAllElements();