我在做一个非常简单的费用追踪器：

public class ExpenseTracker {

JFrame frame;
JPanel mainPanel;
JPanel inputPanel;
JPanel registerPanel;
DefaultTableModel tableModel;
JDatePicker datePicker;
JTextField nameTextField;
JTextField amountTextField;
SimpleDateFormat sdf;
Date date;

public static void main(String[] args) {
    new ExpenseTracker().buildGUI();
}

public void buildGUI() {

    mainPanel = new JPanel();
    inputPanel = new JPanel();
    inputPanel.setLayout(new BoxLayout(inputPanel, BoxLayout.Y_AXIS));
    
    JLabel nameLabel = new JLabel("Name: ");
    nameLabel.setFont(new Font("Arial", Font.ITALIC, 25));
    nameTextField = new JTextField();
    nameTextField.setDocument(new JTextFieldLimit(10));
    JLabel dateLabel = new JLabel("Date: ");
    dateLabel.setFont(new Font("Arial", Font.ITALIC, 25));
    datePicker = new JDatePicker();

    JLabel amountLabel = new JLabel("Amount: ");
    amountLabel.setFont(new Font("Arial", Font.ITALIC, 25));
    amountTextField = new JTextField();
    amountTextField.setDocument(new JTextFieldLimit(5));

    
    JButton addExpense = new JButton("Add");
    addExpense.addActionListener(new addExpenseListener());

    inputPanel.add(nameLabel);
    inputPanel.add(nameTextField);
    inputPanel.add(dateLabel);
    inputPanel.add(datePicker);
    inputPanel.add(amountLabel);
    inputPanel.add(amountTextField);
    inputPanel.add(addExpense);
    
    
    registerPanel = new JPanel();
    tableModel = new DefaultTableModel();
    JTable register = new JTable(tableModel);
    tableModel.addColumn("Name");
    tableModel.addColumn("Date");
    tableModel.addColumn("Amount");
    register.setBackground(Color.LIGHT_GRAY);
    registerPanel.add(register);
    
    
    
    mainPanel.add(BorderLayout.NORTH, inputPanel);
    mainPanel.add(BorderLayout.CENTER, registerPanel);
    frame.add(mainPanel);
    frame.setVisible(true);
    
}

public void addToRegister() {
    String name = nameTextField.getText();
    sdf = new SimpleDateFormat();
    Date dateToFormat = (Date) datePicker.getModel().getValue();
    String date = sdf.format(dateToFormat);
    String amount = amountTextField.getText();
    tableModel.addRow(new Object[] {name, date, amount});
}

省略了一些代码。我得到了一个异常：
无法将类java.util.GregorianCalendar强制转换为类java.util.Date（java.util.GregorianCalendar和java.util.Date位于加载程序“引导”的模块java.base中）
我不知道如何改变它，我知道的是如何从DatePicker中获取日期，这是类冲突的地方，使用jdatepicker库。