运行GoF 定义:为系统中一系列的接口提供一个统一的接口。外观模式定义了一个更高层的接口，使得子系统更容易使用。（ Provide a unified interface to a set of interfaces in a system. Facade defines a higher-level interface that makes the subsystem easier to use.)
进一步解释：外观模式是一种很直白的设计思路，就是用一个类包含多个类对象，以实现统一的调用接口。例如，我们设计一个图形界面程序，写了一堆在桌面上绘制不同图形的类（Line, Ract, Circle等）。然后我们用一个更高层的类（DrawShape）包装这些类，这样用户只需要跟DrawShape打交道即可，简化了程序员需要使用到的接口。反过来，如果我们要设计这样一个图形程序，自上而下的设计方法告诉我们，首先应该写一个总体的接口，然后再考虑细节部分的实现。这就是外观模式。
使用代码来呈现上述的例子：
import java.util.Random; /** * Facade patterns */ // 外观类，提供了三种不同形状的上层接口 class DrawShapeFacade { private Line line; private Circle circle; private Rect rect; public DrawShapeFacade() { this.line = new Line(); this.circle = new Circle(); this.rect = new Rect(); } public void setLinePara(float length) { line.setLength(length); } public void setCirclePara(float radius) { circle.setRadius(radius); } public void setRectPara(float len, float wid) { rect.setLength(len); rect.setWidth(wid); } public void drawAll() { line.draw(); circle.draw(); rect.draw(); } } class Line { private float length; public void setLength(float length) { this.length = length; } public void draw() { System.out.printf("Draw a line, with length %.2f \n", length); } } class Circle { private float radius; public void setRadius(float radius) { this.radius = radius; } public void draw() { System.out.printf("Draw a circle with radius %.2f\n", radius); } } class Rect { private float length; private float width; public void setLength(float length) { this.length = length; } public void setWidth(float width) { this.width = width; } public void draw() { System.out.printf("Draw a rectangular, l=%.2f, w=%.2f\n", length, width); } } public class Main { public static void main(String[] args) { DrawShapeFacade shapeFacade = new DrawShapeFacade(); shapeFacade.setCirclePara(10); shapeFacade.setLinePara(2.13F); shapeFacade.setRectPara(3.2F, 4.0F); shapeFacade.drawAll(); } }运行结果：
程序结构：
