限制JTextField中的字符数

import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.DocumentFilter;

public class Main {
    public static void main(String[] args) {
        JFrame frame = new JFrame("限制JTextField中的字符数");
        JTextField textField = new JTextField(20);

        // 使用DocumentFilter限制字符数
        ((AbstractDocument) textField.getDocument()).setDocumentFilter(new DocumentFilter() {
            private int maxLength = 10; // 限制的字符数

            @Override
            public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr)
                    throws BadLocationException {
                // 当前字符数加上插入的字符数是否超过限制
                if (fb.getDocument().getLength() + string.length() <= maxLength) {
                    super.insertString(fb, offset, string, attr);
                }
            }

            @Override
            public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs)
                    throws BadLocationException {
                // 当前字符数加上替换的字符数减去被删除的字符数是否超过限制
                if (fb.getDocument().getLength() + text.length() - length <= maxLength) {
                    super.replace(fb, offset, length, text, attrs);
                }
            }
        });

        frame.getContentPane().add(textField);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }
}