Structural mode - facade mode

One ： Definition

Also known as facade pattern , It is a method to provide a consistent interface through multiple complex subsystems , Patterns that make these subsystems more accessible .
This mode has a unified interface for me , External applications don't care about the details of the internal subsystem , This will greatly reduce the complexity of the application , Improved program maintainability .

Two ： role

• appearance （Facade） role ： Provide a common interface for multiple subsystems .
• Subsystem （Sub System） role ： Realize some functions of the system , Customers can access it through the facade role .

3、 ... and ： Case study

Operate all smart homes through smart audio .

public class Light {
    
    public void on() {
    
        System.out.println(" Turn on the light ");
    }

    public void off() {
    
        System.out.println(" Turn off the lights ");
    }
}

public class TV {
    
    public void on() {
    
        System.out.println(" Turn on the TV ");
    }

    public void off() {
    
        System.out.println(" Turn off the TV ");
    }
}

AISound： Artificial intelligence sound , It can control all smart appliances . Hold references to all smart appliances , Provide unified external access , And adapt to the operation of each household appliance .

public class AISound {
    
    private Light light;
    private TV tv;

    public AISound() {
    
        light = new Light();
        tv = new TV();
    }

    public void say(String msg) {
    
        if (msg.contains(" open ")) {
    
            light.on();
            tv.on();
        } else if (msg.contains(" close ")) {
    
            light.off();
            tv.off();
        }
    }
}

public class Client {
    
    public static void main(String[] args) {
    
        AISound aiSound = new AISound();
        aiSound.say(" Turn on the appliance ");
        aiSound.say(" Turn off appliances ");
    }
}

Four ： benefits

• advantage ：
  • Reduce the coupling between the subsystem and the client , So that changes to the subsystem do not affect the client class that invokes it .
  • Shielding subsystem components from customers , Reduce the object data processed by customers , And make it easier to use the subsystem .
• shortcoming ：
  • Inconsistent with the open and close principle , Modification is troublesome .

5、 ... and ： Use scenarios

• When building the overall structure system , Using appearance pattern to define the entry point of each layer in a subsystem can simplify the dependency between subsystems .
• When there are many complex subsystems , Appearance mode can design a simple interface for the system for external access .
• When there is a large connection between the client and multiple subsystems , Introducing appearance mode can separate them , So as to improve the independence and portability of the subsystem .