Java JPasswordField中指定的字符数

我的java代码中有一个JPasswordField，我希望JPasswordField只能从用户那里获得7个字符作为输入，但不能超过7个字符。请说明如何执行此操作。

将ActionListener添加到JPasswordField以执行此操作：

 passwordField.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent event) {
        JPasswordField field = (JPasswordField) event.getSource();
        char[] password = field.getPassword();

        if (password.length > 7) {
            System.out.println("Password must contain 7 characters!");
        }
    }
});

或者使用keyListener

passwordField.addKeyListener(new KeyAdapter() {
    @Override
    public void keyReleased(KeyEvent event) {
        JPasswordField field = (JPasswordField) event.getSource();
        char[] password = field.getPassword();

        if (password.length > 7) {
            System.out.println("Password must contain 7 characters!");
        }
    }
});

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这不会阻止用户输入超过7个字符，如用户3808922要求的字符。他应该使用KeyListener并监听keyTyped事件。这样他就可以对密码字段中输入的每个字符做出反应。