template

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

enum TYPEPANEL {AUTH, REGISTER, DOWNLOAD};

public class Template {

    public static void main(String[] args) {
        new Window();
    }

}

class Window extends JFrame {

    private AuthPanel authPanel;
    private RegisterPanel registerPanel;
    private DownLoadPanel downloadPanel;


    private TYPEPANEL typePanel = TYPEPANEL.AUTH;

    public void setVisiblePanel(TYPEPANEL type)
    {
        authPanel.setVisible(false);
        registerPanel.setVisible(false);
        downloadPanel.setVisible(false);

        switch (type)
        {
        case REGISTER:
                setRegisterPanel();
                break;
        case DOWNLOAD:
                setDownloadPanel();
                break;
        default:
                setAuthPanel();
        }
    }


    private void setAuthPanel() {
        typePanel = TYPEPANEL.AUTH;
        setContentPane(authPanel);
        setTitle(authPanel.getTitle());
        authPanel.setVisible(true);
    }

    private void setRegisterPanel() {
        typePanel = TYPEPANEL.REGISTER;
        setContentPane(registerPanel);
        setTitle(registerPanel.getTitle());
        registerPanel.setVisible(true);
    }

    private void setDownloadPanel() {
        typePanel = TYPEPANEL.DOWNLOAD;
        setContentPane(downloadPanel);
        setTitle(downloadPanel.getTitle());
        downloadPanel.setVisible(true);
    }

    public Window() {

        //создаем все возможные панели, но загружаем только одну
        authPanel = new AuthPanel(this);
        registerPanel = new RegisterPanel(this);
        downloadPanel = new DownLoadPanel(this);

        setLayout(null);
        setAuthPanel();
        setBounds(0,0,500,600);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }
}

//форма авторизации
class AuthPanel extends JPanel {

    private Window wnd;//ссылка на родителя (JFrame)

    public String getTitle() { return "Авторизация";}

    JTextField txtLoginName = new JTextField();

    public AuthPanel(Window refParent) {

        wnd = refParent;

        setLayout(null);

        txtLoginName.setBounds(10, 10, 100, 30);
        add(txtLoginName);

        JButton btnAdd = new JButton("Подключиться");
        btnAdd.setBounds(100, 100, 200, 50);
        add(btnAdd);

        btnAdd.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {

                String login = txtLoginName.getText().trim();

                if (login.equals("admin"))
                {
                    wnd.setVisiblePanel(TYPEPANEL.DOWNLOAD);
                } else //на форму регистрации
                wnd.setVisiblePanel(TYPEPANEL.REGISTER);
            }
        });

        setBounds(0,0,200,200);
        setVisible(false); //по умолчанию прячем
    }
}

//форма регистрации
class RegisterPanel extends JPanel {

    private Window wnd;//ссылка на родителя (JFrame)

    JTextField txtLoginName = new JTextField();


    public String getTitle() { return "Регистрация";}

    public RegisterPanel(Window refParent) {

        wnd = refParent;

        setLayout(null);
        JButton btnAdd = new JButton("Зарегистрироваться");
        btnAdd.setBounds(100, 100, 200, 50);



        add(btnAdd);
        setBounds(0,0,200,200);
        setVisible(false); //по умолчанию прячем
    }
}

//форма для закачки игр
class DownLoadPanel extends JPanel {

    private Window wnd;//ссылка на родителя (JFrame)

    public String getTitle() { return "Загрузка файлов";}

    public DownLoadPanel(Window refParent) {

        wnd = refParent;

        setLayout(null);
        JButton btnDownload = new JButton("Загрузить игру");
        btnDownload.setBounds(50, 100, 200, 50);
        add(btnDownload);
        setBounds(0,0,200,200);
        setVisible(false); //по умолчанию прячем
    }
}