Design Pattern 简明教程

Design Patterns - Facade Pattern

外观模式隐藏了系统的复杂性，并向客户端提供了一个接口，客户端使用该接口可以访问系统。这类设计模式属于结构型模式，因为此模式向现有系统添加了一个接口以隐藏其复杂性。

Facade pattern hides the complexities of the system and provides an interface to the client using which the client can access the system. This type of design pattern comes under structural pattern as this pattern adds an interface to existing system to hide its complexities.

该模式包含一个单一的类，提供客户端所需的简化方法，并将调用委托给现有系统类的函数。

This pattern involves a single class which provides simplified methods required by client and delegates calls to methods of existing system classes.

Implementation

我们将创建一个 Shape 接口和一个实现 Shape 接口的具体类。下一步，将定义一个外观类 ShapeMaker。

We are going to create a Shape interface and concrete classes implementing the Shape interface. A facade class ShapeMaker is defined as a next step.

ShapeMaker 类使用具体类将用户调用委托给这些类。我们的演示类 FacadePatternDemo 将使用 ShapeMaker 类展示结果。

ShapeMaker class uses the concrete classes to delegate user calls to these classes. FacadePatternDemo, our demo class, will use ShapeMaker class to show the results.

facade pattern uml diagram

Step 1

创建一个接口。

Create an interface.

Shape.java

public interface Shape {
   void draw();
}

Step 2

创建实现相同接口的具体类。

Create concrete classes implementing the same interface.

Rectangle.java

public class Rectangle implements Shape {

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

Square.java

public class Square implements Shape {

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

Circle.java

public class Circle implements Shape {

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

Step 3

创建一个外观类。

Create a facade class.

ShapeMaker.java

public class ShapeMaker {
   private Shape circle;
   private Shape rectangle;
   private Shape square;

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

   public void drawCircle(){
      circle.draw();
   }
   public void drawRectangle(){
      rectangle.draw();
   }
   public void drawSquare(){
      square.draw();
   }
}

Step 4

使用外观来绘制各种形状。

Use the facade to draw various types of shapes.

FacadePatternDemo.java

public class FacadePatternDemo {
   public static void main(String[] args) {
      ShapeMaker shapeMaker = new ShapeMaker();

      shapeMaker.drawCircle();
      shapeMaker.drawRectangle();
      shapeMaker.drawSquare();
   }
}

Step 5

验证输出。

Verify the output.

Circle::draw()
Rectangle::draw()
Square::draw()