Mediator Pattern - Example

Example

In the following example a mediator object controls the status of three collaborating buttons: for this it contains three methods (book,view and search) that set the status of the buttons. The methods are called by each button upon activation (via the execute method in each of them).

Hence here the collaboration pattern is that each participant (here the buttons) communicates to the mediator its activity and the mediator dispatches the expected behavior to the other participants.

import java.awt.Font; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; //Colleague interface interface Command { void execute; } //Abstract Mediator interface IMediator { void book; void view; void search; void registerView(BtnView v); void registerSearch(BtnSearch s); void registerBook(BtnBook b); void registerDisplay(LblDisplay d); } //Concrete mediator class Mediator implements IMediator { 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..."); } } //A concrete colleague class BtnView extends JButton implements Command { IMediator med; BtnView(ActionListener al, IMediator m) { super("View"); addActionListener(al); med = m; med.registerView(this); } public void execute { med.view; } } //A concrete colleague class BtnSearch extends JButton implements Command { IMediator med; BtnSearch(ActionListener al, IMediator m) { super("Search"); addActionListener(al); med = m; med.registerSearch(this); } public void execute { med.search; } } //A concrete colleague class BtnBook extends JButton implements Command { IMediator med; BtnBook(ActionListener al, IMediator m) { super("Book"); addActionListener(al); med = m; med.registerBook(this); } public void execute { med.book; } } class LblDisplay extends JLabel { IMediator med; LblDisplay(IMediator m) { super("Just start..."); med = m; med.registerDisplay(this); setFont(new Font("Arial", Font.BOLD, 24)); } } class MediatorDemo extends JFrame implements ActionListener { IMediator med = new Mediator; MediatorDemo { JPanel p = new JPanel; p.add(new BtnView(this, med)); p.add(new BtnBook(this, med)); p.add(new BtnSearch(this, med)); getContentPane.add(new LblDisplay(med), "North"); getContentPane.add(p, "South"); setSize(400, 200); setVisible(true); } public void actionPerformed(ActionEvent ae) { Command comd = (Command) ae.getSource; comd.execute; } public static void main(String args) { new MediatorDemo; } }