Mediator pattern - Example

If you have a complex GUI, whenever a button has been clicked, the related actions should be disabled or enabled. You may design a Mediator class to include all related classes : 

interface Command {

    void execute();

}

class Mediator {

    BtnView btnView;

    BtnSearch btnSearch;

    BtnBook btnBook;

    LblDisplay show;

    //....

    void registerView(BtnView v) {

        btnView = v;

    }

    void registerSearch(BtnSearch s) {

        btnSearch = s;

    }

    void registerBook(BtnBook b) {

        btnBook = b;

    }

    void registerDisplay(LblDisplay d) {

        show = d;

    }

    void book() {

       btnBook.setEnabled(false);

       btnView.setEnabled(true);

       btnSearch.setEnabled(true);

       show.setText("booking...");

    }

    void view() {

       btnView.setEnabled(false);

       btnSearch.setEnabled(true);

       btnBook.setEnabled(true);

       show.setText("viewing...");

    }

    void search() {

       btnSearch.setEnabled(false);

       btnView.setEnabled(true);

       btnBook.setEnabled(true);

       show.setText("searching...");

    }

}

Then, you may define classes which should be controlled by the Mediator class.

class BtnXYZ extends JButton implements Command {

    Mediator med;

    BtnXYZ(ActionListener al, Mediator m) {

        super("View");

        // super("Search");

        // super("Book");

        addActionListener(al);

        med = m;

        med.registerView(this);

        // med.registerSearch(this);

        // med.registerBook(this);

    }

    public void execute() {

       med.view();

       // med.search();

       // med.book();

    }

}