在JFormattedTextField中输入日期后，自定义掩码消失

import javax.swing.*;
import javax.swing.text.*;
import java.text.*;

public class CustomDateFormatter extends AbstractFormatter {
    private SimpleDateFormat dateFormatter;

    public CustomDateFormatter(String pattern) {
        dateFormatter = new SimpleDateFormat(pattern);
    }

    @Override
    public Object stringToValue(String text) throws ParseException {
        return dateFormatter.parseObject(text);
    }

    @Override
    public String valueToString(Object value) throws ParseException {
        if (value instanceof java.util.Date) {
            return dateFormatter.format((java.util.Date) value);
        }
        throw new ParseException("Invalid type", 0);
    }
}

import javax.swing.*;
import java.awt.*;
import java.text.ParseException;

public class MainFrame extends JFrame {
    public MainFrame() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 200);
        setLocationRelativeTo(null);

        JFormattedTextField textField = new JFormattedTextField(new CustomDateFormatter("yyyy-MM-dd"));
        textField.setColumns(10);

        getContentPane().setLayout(new FlowLayout());
        getContentPane().add(textField);

        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new MainFrame());
    }
}