設計模式（17）——Mediator(中介者）

中介者模式是什麼？

中介者模式用一箇中介對象來封裝一系列的對象交互。中介者使各對象不需要顯示地相互引用，從而使其耦合鬆散，而且可以獨立地改變它們之間的交互。

中介者模式封裝了對象之間的通信。對象不再直接通信，而是通過中介者通信。

中介者模式的示例

下面以飛機着陸爲例說明Mediator的應用，在例子中，飛機和跑道不直接通信，而是通過mediator處理。

public interface IATCMediator {

	public void registerRunway(Runway runway);

	public void registerFlight(Flight flight);

	public boolean isLandingOk();

	public void setLandingStatus(boolean status);
}

public class ATCMediator implements IATCMediator {
	private Flight flight;
	private Runway runway;
	public boolean land;

	public void registerRunway(Runway runway) {
		this.runway = runway;
	}

	public void registerFlight(Flight flight) {
		this.flight = flight;
	}

	public boolean isLandingOk() {
		return land;
	}

	@Override
	public void setLandingStatus(boolean status) {
		land = status;

	}
}

public interface Command {
	void land();
}

public class Flight implements Command {
	private IATCMediator atcMediator;

	public Flight(IATCMediator atcMediator) {
		this.atcMediator = atcMediator;
	}

	public void land() {
		if (atcMediator.isLandingOk()) {
			System.out.println("Landing done....");
			atcMediator.setLandingStatus(true);
		} else
			System.out.println("Will wait to land....");
	}

	public void getReady() {
		System.out.println("Getting ready...");
	}

}

public class Runway implements Command {
	private IATCMediator atcMediator;

	public Runway(IATCMediator atcMediator) {
		this.atcMediator = atcMediator;
		atcMediator.setLandingStatus(true);
	}

	@Override
	public void land() {
		System.out.println("Landing permission granted...");
		atcMediator.setLandingStatus(true);
	}

}

public class MediatorDesignPattern {
	public static void main(String args[]) {

		IATCMediator atcMediator = new ATCMediator();
		Flight sparrow101 = new Flight(atcMediator);
		Runway mainRunway = new Runway(atcMediator);
		atcMediator.registerFlight(sparrow101);
		atcMediator.registerRunway(mainRunway);
		sparrow101.getReady();
		mainRunway.land();
		sparrow101.land();
	}
}

鏈接：http://javapapers.com/design-patterns/mediator-design-pattern/