如何用泛型实现观察者模式？

Question

我正在制作一个餐厅应用程序，我需要使用泛型类型参数。工作流程如下：客户机（观察者）订购食物（界面），FoodFactory返回具体类型（如热狗、薯片等），然后客户机（观察者）收到通知。我需要在这个练习中使用一些课程。在本练习中，类型参数

public abstract class Observable<E>{

List<Observer<E>> observers = new ArrayList<>();

public void abbObserver(Observer <E> e){
 observers.add(e);
}

public void notifyObservers(E e){
    for(Observer observer : observers){
        observer.update(this);
    }
}

}

该类由顺序类继承。

public class Order<E> extends Observable<E> {

    private FoodName food;
    private List<FoodName> extras;


    public Order(FoodName food, List<FoodName> extras) {
            this.food = food;
            this.extras = extras;
    }

    public FoodName getFood() {
            return food;
    }

    public List<FoodName> getExtras() {
            return extras;
    }

    @Override
    public void abbObserver(Observer<E> e) {
            super.abbObserver(e);
    }

    @Override
    public void notifyObservers(E e) {
            System.out.println("Notifying Observers of: " + e.toString());
    }

然而，我不确定如何才能做到这一点。我需要继承列表吗




Answer 1

我想你的意思是：

public class FoodName {
  private final String name;

  public FoodName(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }
}

public class Order extends Observable<FoodName> {

  private FoodName food;
  private List<FoodName> extras = new ArrayList<>();

  public Order(FoodName food, List<FoodName> extras) {
    this.food = food;
    this.extras = extras;
  }

  public FoodName getFood() {
    return food;
  }

  public List<FoodName> getExtras() {
    return extras;
  }

  public void addExtras(FoodName extra) {
    extras.add(extra);
    notifyObservers(extra);
  }

}

public interface Observer<E> {
  void update(E e);
}

public class Main {
  public static void main(String[] args) {
    Order order = new Order(new FoodName("bigmac"), new ArrayList<>());
    order.abbObserver(fn -> System.out.println(fn.getName()));
    order.addExtras(new FoodName("french fries"));
  }
}