外觀模式能降低訪問複雜系統的內部子系統時的複雜度，簡化客戶端與之互動的介面，為多個子系統對外提供一個共同的介面。

1、多個子系統

public class Circle {
    public void draw() {
        System.out.println("Circle::draw()");
    }
}

public class Rectangle {
    public void draw() {
        System.out.println("Rectangle::draw()");
    }
}

public class Square {
    
 
public void draw() {
        System.out.println("Square::draw()");
    }
}

2、定義Facade

public class ShapeFacade {
    private Circle circle;
    private Rectangle rectangle;
    private Square square;

    public ShapeFacade() {
        circle = new Circle();
        rectangle = new Rectangle();
        square 
 
= new Square();
    }

    public void drawCircle() {
        circle.draw();
    }

    public void drawRectangle() {
        rectangle.draw();
    }

    public void drawSquare() {
        square.draw();
    }
}

3、測試

public class _Test {
    public static void main(String[] args) {
        ShapeFacade shapeMaker 
 
= new ShapeFacade();
        shapeMaker.drawCircle();
        shapeMaker.drawRectangle();
        shapeMaker.drawSquare();
    }
}

通過ShapeFacade就可以訪問各個子系統。