Java Swing - 如何使用DocumentFilter创建JFormattedTextField的自定义格式

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class Main {
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JPanel contentPane = new JPanel();
    JTextField tField = new JTextField(10);
    ((AbstractDocument) tField.getDocument())
        .setDocumentFilter(new MyDocumentFilter());
    contentPane.add(tField);

    frame.setContentPane(contentPane);
    frame.pack();
    frame.setVisible(true);
  }
}

class MyDocumentFilter extends DocumentFilter {
  @Override
  public void insertString(DocumentFilter.FilterBypass fp, int offset,
      String string, AttributeSet aset) throws BadLocationException {
    int len = string.length();
    boolean isValidInteger = true;

    for (int i = 0; i < len; i++) {
      if (!Character.isDigit(string.charAt(i))) {
        isValidInteger = false;
        break;
      }
    }
    if (isValidInteger) {
      super.insertString(fp, offset, string, aset);
    } else {
      System.out.println("not valid integer");
    }
  }

  @Override
  public void replace(DocumentFilter.FilterBypass fp, int offset, int length,
      String string, AttributeSet aset) throws BadLocationException {
    int len = string.length();
    boolean isValidInteger = true;
    for (int i = 0; i < len; i++) {
      if (!Character.isDigit(string.charAt(i))) {
        isValidInteger = false;
        break;
      }
    }
    if (isValidInteger) {
      super.replace(fp, offset, length, string, aset);
    } else {
      System.out.println("not valid integer");
    }
  }
}