要解决您的问题，您需要使用观察者模式，在对象之间进行特定的通信，这意味着任何更改发生在已验证的字段中，它将通知主类。
你可以阅读更多关于这个模式The Observer Pattern in Java
主登录类：

public class MainLogin implements PropertyChangeListener {
    private static boolean authenticated;
      public static void main(String[] args) {
            Login login = new Login();
            MainLogin observer = new MainLogin();
            login.authenticated.addPropertyChangeListener(observer);
        }
    
        @Override
        public void propertyChange(PropertyChangeEvent evt) {
            this.authenticated = (boolean) evt.getNewValue();
            if (this.authenticated)
                System.exit(0);
        }
    }

PCLauth分类：

public class PCLauth  {

    private boolean authenticated;
    private PropertyChangeSupport support;

     public PCLauth () {
         support = new PropertyChangeSupport(this);
     }

    public void addPropertyChangeListener(PropertyChangeListener pcl) {
        support.addPropertyChangeListener(pcl);
    }

    public void removePropertyChangeListener(PropertyChangeListener pcl) {
        support.removePropertyChangeListener(pcl);
    }

   public void authenticate(boolean state) {
        support.firePropertyChange("authenticated", this.authenticated, state);
        this.authenticated = state;
   }

登录类：

public class Login {
    
        private  JTextField usr_field;
        private  JLabel title;
        private  JButton login_btn;
        private  JPasswordField pwd_field;
        private  String usr = "admin";
        private static String pass = "pass";
    
        public  PCLauth authenticated;
    
        public Login() {
            this.authenticated = new PCLauth();
            buildGui();
        }
    
        /**
         * @wbp.parser.entryPoint
         *
         *
         */
    
    
        private  void buildGui()
        {
            JFrame frame = new JFrame();
            GridBagConstraints c = new GridBagConstraints();
            c.fill = GridBagConstraints.HORIZONTAL;
            c.weightx = 0.5;
            c.weighty = 0.5;
            c.gridx = 1;
            c.gridy = 0;
    
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
            frame.getContentPane().setBackground(new Color(74, 74, 74));
            frame.getContentPane().setLayout(new GridBagLayout());
            frame.setTitle("Login");
    
            JPanel panel = new JPanel(new GridBagLayout( ));
            panel.setBackground(new Color(74, 74, 74));
            frame.getContentPane().add(panel);
            JLabel username = new JLabel("User name");
            panel.add(username, c);
            c.gridx++;
            usr_field = new JTextField();
            panel.add(usr_field, c);
            usr_field.setColumns(10);
    
            c.gridx = 1;
            c.gridy = 1;
    
            title = new JLabel("password");
            panel.add(title, c);
    
    
            c.gridx++;
    
            pwd_field = new JPasswordField();
    
    
            panel.add(pwd_field, c);
    
            c.gridx = 1;
            c.gridy = 4;
    
            login_btn = new JButton("Login");
            login_btn.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    char[] inputPass = pwd_field.getPassword();
                    char[] appPass = Login.pass.toCharArray();
                    if (Arrays.equals(inputPass, appPass) && usr.equals(usr_field.getText())) {
                        System.out.println( SwingUtilities.isEventDispatchThread()  + ", " +Thread.currentThread().getName());
    
                        authenticated.authenticate(true);
    
                    }
                    else {
                        authenticated.authenticate(false);
                        JOptionPane.showMessageDialog(panel, "Obs,your username or password is incorrect!");
                    }
                }
            });
            panel.add(login_btn, c);
            frame.setSize(new Dimension(500, 500));
            frame.setVisible(true);
            frame.setResizable(false);
    
        }
    }