Mediator

Table of content

• Abstract Factory

• Builder

• Factory method

• Prototype

• Singleton

• Adapter

• Bridge

• Composite

• Decorator

• Facade

• Flyweight

• Proxy

• Chain of responsibility

• Command

• Interpreter

• Iterator

• Mediator

• Memento

• Observer

• State

• Strategy

• Template method

• Visitor

• Model–view–controller

This pattern helps to model a class whose object at run-time is responsible for controlling and coordinating the interactions of a group of other objects.

Participants

Mediator - defines the interface for communication between Colleague objects.

ConcreteMediator - implements the Mediator interface and coordinates communication between Colleague objects. It is aware of all the Colleagues and their purpose with regards to inter communication.

ConcreteColleague - communicates with other Colleagues through its Mediator.

Implementation in Java

// Colleague interface
interface Command {
    void execute();
}

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;
 
// Concrete mediator
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...");
    }
 
}

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;
// A concrete colleague
class BtnView extends JButton implements Command {
 
    Mediator med;
 
    BtnView(ActionListener al, Mediator m) {
        super("View");
        addActionListener(al);
        med = m;
        med.registerView(this);
    }
 
    public void execute() {
        med.view();
    }
 
}

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;
 
// A concrete colleague
class BtnSearch extends JButton implements Command {
 
    Mediator med;
 
    BtnSearch(ActionListener al, Mediator m) {
        super("Search");
        addActionListener(al);
        med = m;
        med.registerSearch(this);
    }
 
    public void execute() {
        med.search();
    }
 
}

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;
 
// A concrete colleague
class BtnBook extends JButton implements Command {
 
    Mediator med;
 
    BtnBook(ActionListener al, Mediator m) {
        super("Book");
        addActionListener(al);
        med = m;
        med.registerBook(this);
    }
 
    public void execute() {
        med.book();
    }
 
}

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;
 
class LblDisplay extends JLabel {
 
    Mediator med;
 
    LblDisplay(Mediator m) {
        super("Just start...");
        med = m;
        med.registerDisplay(this);
        setFont(new Font("Arial", Font.BOLD, 24));
    }
 
}

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;
 
class MediatorDemo extends JFrame implements ActionListener {
 
    Mediator 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();
    }
 
}

Implementation in C#

using System;
using System.Collections;
 
  class MainApp
  {
    static void Main()
    {
      ConcreteMediator m = new ConcreteMediator();
 
      ConcreteColleague1 c1 = new ConcreteColleague1(m);
      ConcreteColleague2 c2 = new ConcreteColleague2(m);
 
      m.Colleague1 = c1;
      m.Colleague2 = c2;
 
      c1.Send("How are you?");
      c2.Send("Fine, thanks");
 
      // Wait for user
      Console.Read();
    }
  }
 
  // "Mediator"
  abstract class Mediator
  {
    public abstract void Send(string message,
      Colleague colleague);
  }
 
  // "ConcreteMediator"
  class ConcreteMediator : Mediator
  {
    private ConcreteColleague1 colleague1;
    private ConcreteColleague2 colleague2;
 
    public ConcreteColleague1 Colleague1
    {
      set{ colleague1 = value; }
    }
 
    public ConcreteColleague2 Colleague2
    {
      set{ colleague2 = value; }
    }
 
    public override void Send(string message,
      Colleague colleague)
    {
      if (colleague == colleague1)
      {
        colleague2.Notify(message);
      }
      else
      {
        colleague1.Notify(message);
      }
    }
  }
 
  // "Colleague"
  abstract class Colleague
  {
    protected Mediator mediator;
 
    // Constructor
    public Colleague(Mediator mediator)
    {
      this.mediator = mediator;
    }
  }
 
  // "ConcreteColleague1"
  class ConcreteColleague1 : Colleague
  {
    // Constructor
    public ConcreteColleague1(Mediator mediator)
      : base(mediator)
    {
    }
 
    public void Send(string message)
    {
      mediator.Send(message, this);
    }
 
    public void Notify(string message)
    {
      Console.WriteLine("Colleague1 gets message: "
        + message);
    }
  }
 
  // "ConcreteColleague2"
  class ConcreteColleague2 : Colleague
  {
    // Constructor
    public ConcreteColleague2(Mediator mediator)
      : base(mediator)
    {
    }
 
    public void Send(string message)
    {
      mediator.Send(message, this);
    }
 
    public void Notify(string message)
    {
      Console.WriteLine("Colleague2 gets message: "
        + message);
    }
  }