Coordinating Your Objects with the Mediator Patterns : Mediator Pattern « Design Pattern « Java Tutorial

1. Java Tutorial
2. Design Pattern
3. Mediator Pattern

public class Mediator {
  Welcome welcome;
  Browse browse;
  Purchase purchase;
  Exit exit;

  public Mediator() {
    welcome = new Welcome(this);
    browse = new Browse(this);
    purchase = new Purchase(this);
    exit = new Exit(this);
  }

  public void handle(String state) {
    if (state.equals("welcome.shop")) {
      browse.execute();
    } else if (state.equals("shop.purchase")) {
      purchase.execute();
    } else if (state.equals("purchase.exit")) {
      exit.execute();
    } else if (state.equals("welcome.exit")) {
      exit.execute();
    } else if (state.equals("shop.exit")) {
      exit.execute();
    } else if (state.equals("purchase.exit")) {
      exit.execute();
    }
  }

  public Welcome getWelcome() {
    return welcome;
  }
  public static void main(String args[]) {
    Mediator mediator = new Mediator();
    mediator.getWelcome().execute();
  }

}

class Exit {
  Mediator mediator;

  public Exit(Mediator m) {
    mediator = m;
  }

  public void execute() {
    System.out.println("exit");
  }
}

class Browse {
  Mediator mediator;

  public Browse(Mediator m) {
    mediator = m;
  }

  public void execute() {
    mediator.handle("shop.purchase");
    mediator.handle("shop.exit");
  }
}

class Welcome {
  Mediator mediator;

  public Welcome(Mediator m) {
    mediator = m;
  }

  public void execute() {
    mediator.handle("welcome.shop");
    mediator.handle("welcome.exit");
  }
}

class Purchase {
  Mediator mediator;

  public Purchase(Mediator m) {
    mediator = m;
  }

  public void execute() {
    System.out.println("Thanks for your purchase.");
    mediator.handle("purchase.exit");
  }
}