Giovanny's WikiMediator
The mediator pattern is a behavioral design pattern that defines an object that encapsulates how a set of objects interact. This pattern is considered to be a behavioral pattern due to the way it can alter the program's running behavior.
Key Points
- The mediator pattern is a behavioral design pattern.
- The mediator pattern defines an object that encapsulates how a set of objects interact.
- The mediator pattern is used to reduce coupling between classes that communicate with each other.
- The mediator pattern is used when a set of objects communicate in well-defined but complex ways.
- The mediator pattern is used when reusing an object is difficult because it refers to many other objects and these objects refer to it.
Use Cases
- Reduce coupling between classes that communicate with each other.
- Reduce chaotic dependencies between classes.
- Encapsulate complex communication between a set of objects.
- Reuse an object that refers to many other objects and these objects refer to it.
Class Diagram
+-------------------+
| <<interface>> |
| Mediator |
+-------------------+
| + send(message, |
| colleague) |
+-------------------+
^
|
| implements
|
+-------------------+
| ConcreteMediator |
+-------------------+
| + send(message, |
| colleague) |
+-------------------+
| - colleague1 |
| - colleague2 |
+-------------------+
/ \
/ \
/ \
+-------------------+ +-------------------+
| Colleague1 | | Colleague2 |
+-------------------+ +-------------------+
| - mediator | | - mediator |
+-------------------+ +-------------------+
| + send(message) | | + send(message) |
| + receive(message)| | + receive(message)|
+-------------------+ +-------------------+ +-------------------+
| <<interface>> |
| Mediator |
+-------------------+
| + send(message, |
| colleague) |
+-------------------+
^
|
| implements
|
+-------------------+
| ConcreteMediator |
+-------------------+
| + send(message, |
| colleague) |
+-------------------+
| - colleague1 |
| - colleague2 |
+-------------------+
/ \
/ \
/ \
+-------------------+ +-------------------+
| Colleague1 | | Colleague2 |
+-------------------+ +-------------------+
| - mediator | | - mediator |
+-------------------+ +-------------------+
| + send(message) | | + send(message) |
| + receive(message)| | + receive(message)|
+-------------------+ +-------------------+Example
- Scenario:
- A chat room is the mediator.
- Users are the colleagues.
- Users can send messages to the chat room, and the chat room will broadcast the message to all users.
- Users can send private messages to other users, and the chat room will deliver the message to the intended user.
java
import java.util.ArrayList;
import java.util.List;
public class Main {
static interface Mediator {
void sendMessage(String message, Colleague colleague);
}
static class ChatRoom implements Mediator {
private List<Colleague> colleagues;
public ChatRoom() {
colleagues = new ArrayList<>();
}
public void addColleague(Colleague colleague) {
colleagues.add(colleague);
}
@Override
public void sendMessage(String message, Colleague colleague) {
for (Colleague c : colleagues) {
if (c != colleague) {
c.receiveMessage(message);
}
}
}
}
static abstract class Colleague {
protected Mediator mediator;
public Colleague(Mediator mediator) {
this.mediator = mediator;
}
public void sendMessage(String message) {
mediator.sendMessage(message, this);
}
public abstract void receiveMessage(String message);
}
static class User extends Colleague {
private String name;
public User(String name, Mediator mediator) {
super(mediator);
this.name = name;
}
@Override
public void receiveMessage(String message) {
System.out.println(name + " received: " + message);
}
}
public static void main(String[] args) {
ChatRoom chatRoom = new ChatRoom();
User user1 = new User("User 1", chatRoom);
User user2 = new User("User 2", chatRoom);
User user3 = new User("User 3", chatRoom);
chatRoom.addColleague(user1);
chatRoom.addColleague(user2);
chatRoom.addColleague(user3);
user1.sendMessage("Hello, everyone!");
user2.sendMessage("Hi, User 1!");
user3.sendMessage("Hey, User 1!");
}
}
import java.util.ArrayList;
import java.util.List;
public class Main {
static interface Mediator {
void sendMessage(String message, Colleague colleague);
}
static class ChatRoom implements Mediator {
private List<Colleague> colleagues;
public ChatRoom() {
colleagues = new ArrayList<>();
}
public void addColleague(Colleague colleague) {
colleagues.add(colleague);
}
@Override
public void sendMessage(String message, Colleague colleague) {
for (Colleague c : colleagues) {
if (c != colleague) {
c.receiveMessage(message);
}
}
}
}
static abstract class Colleague {
protected Mediator mediator;
public Colleague(Mediator mediator) {
this.mediator = mediator;
}
public void sendMessage(String message) {
mediator.sendMessage(message, this);
}
public abstract void receiveMessage(String message);
}
static class User extends Colleague {
private String name;
public User(String name, Mediator mediator) {
super(mediator);
this.name = name;
}
@Override
public void receiveMessage(String message) {
System.out.println(name + " received: " + message);
}
}
public static void main(String[] args) {
ChatRoom chatRoom = new ChatRoom();
User user1 = new User("User 1", chatRoom);
User user2 = new User("User 2", chatRoom);
User user3 = new User("User 3", chatRoom);
chatRoom.addColleague(user1);
chatRoom.addColleague(user2);
chatRoom.addColleague(user3);
user1.sendMessage("Hello, everyone!");
user2.sendMessage("Hi, User 1!");
user3.sendMessage("Hey, User 1!");
}
}