装饰模式（Decorator）

装饰模式（Decorator）：动态地给一个对象添加一些额外的职责，就增加功能来说，装饰模式比生成子类更为灵活。

场景

假设老王有个4S店，卖车。卖的有宝马BMW和特斯拉的ModelX。客户可以从网上下单。小张要写一个销售系统。客户可以定制自己的爱车，例如加皮座椅，和定制音响设备。

赵四买了个ModelX，想要改装音响系统。

刘能看赵四买了ModelX，他想我也得整一个呀！刘能买了一个新的BMW，要装真皮座椅，和更牛的音响系统，让全村人都知道他刘能。

如果你是小张，如何实现这个系统呢？

装饰模式

decorator

代码

Client

public class Client {

  public static void main(String[] args) {
    ICar bmw = new BMW();
    bmw.makeOrder();
//    A new order has been made.Car: u006.BMW

    // decorate
    ICar bmw_leather = new LeatherSeats(bmw);
    ICar bmw_addAudio = new AudioDecorator(bmw_leather);
    bmw_addAudio.makeOrder();
//    A new order has been made.Car: u006.BMW
//    Leather seats have been added.
//    Audio devices are awesome.

    ICar modelX = new ModelX();
    modelX.makeOrder();
//    A new order has been made. Car: u006.ModelX

    // decorate
    ICar modelX_audio = new AudioDecorator(modelX);
    modelX_audio.makeOrder();
//    A new order has been made. Car: u006.ModelX
//    Audio devices are awesome.

  }
}

package u006;

/**
 * Created by HuGuodong on 11/20/19.
 */
public interface ICar {

  void makeOrder();
}

class ModelX implements ICar {

  @Override
  public void makeOrder() {
    System.out.println("A new order has been made. Car: " + this.getClass().getName());
  }
}

class BMW implements ICar {

  @Override
  public void makeOrder() {
    System.out.println("A new order has been made.Car: " + this.getClass().getName());
  }
}

abstract class CarDecorator implements ICar{

  protected ICar car;

  public CarDecorator(ICar car) {
    this.car = car;
  }

  public abstract void makeOrder();

}

class AudioDecorator extends CarDecorator {

  public AudioDecorator(ICar car) {
    super(car);
  }

  @Override
  public void makeOrder() {
    car.makeOrder();
    showAudioDevices();
  }

  public void showAudioDevices(){
    System.out.println("Audio devices are awesome.");
  }

}

class LeatherSeats extends CarDecorator {

  public LeatherSeats(ICar car) {
    super(car);
  }

  @Override
  public void makeOrder() {
    car.makeOrder();
    addLeatherSeats();
  }

  private void addLeatherSeats(){
    System.out.println("Leather seats have been added.");
  }
}