public class Test2 extends JFrame {
    JPanel pane;
    JTextField text;
    JLabel str;

    public Test2() {
        super("字符输入限制");
        pane = new JPanel();
        getContentPane().add(pane);
        text = new JTextField(12);
        str = new JLabel("最多可输入   5   个字符：");
        text.addKeyListener(new KeyListener() {
            public void keyTyped(KeyEvent e) {
                if (text.getText().length() > 4 && e.getKeyChar() != '\b')
                    e.setKeyChar('\0');
            }

            public void keyPressed(KeyEvent e) {
            }

            public void keyReleased(KeyEvent e) {
            }
        });
        pane.add(str);
        pane.add(text);

    }

    public static void main(String[] args) {
        SwingConsole.run(new Test2(), 200, 200);
    }
}