Question

我正在阅读观察者模式设计，并且无法理解一个类如何调用另一个类的方法的方法背后的逻辑，哪个方法不是另一个类的父/子方法。

例如，我有以下公司和员工类。

public class Company {
    String  name;

    public void hire() {
        System.out.println("company hires employees");
    }
}

class Employee {
    int age;
    String  name;

    public void gotHired() {
        System.out.println("employee got hired by a company");
    }
}

这些课程是否有可能采用彼此的方法以便他们进行交流。您可以添加任何有助于解释的方法。谢谢

Answer 1

一个类应该包含其他类Object的引用才能这样做

public class Company {
    String  name;
    Employee employee=new Employee();

    public void hire() {
        System.out.println("company hires employees");
    }
}

通过这种方式，公司类对象可以使用Employee类方法

祝你好运！

Answer 2

是。他们可以沟通。一家公司可以有几个员工。所以，

public class Company {
    String  name;
    List<Employee> empList = new ArrayList<Employee>();  // list of employees belonging to the company. "Composition" 

    public void hire() {
        System.out.println("company hires employees");
    }
    public void addEmployee(Employee e){ // add employee to company. I just got Hired!!!
    empList.add(e);
    }

    String getFirstEmployee(){ // get first employee
     if(!empList.isEmpty){
     Employee e = empList.get(0);
      return e
    }
   }




}

class Employee {
    int age;
    String  name;

    public void gotHired() {
        System.out.println("employee got hired by a company");
    }
}

Answer 3

这是观察者实施。首先是界面：

public interface Observer
{
    public void notifyMe();
}

然后谁想要得到通知：

public class Player implements Observer
{
    @Override public void notifyMe() {
        /* do something */
    }
}

public class Judge implements Observer
{
    @Override public void notifyMe() {
        /* do something */
    }
}

然后由谁负责通知：

public class Game
{
    private ArrayList<Observer> listOfObserver;


    public Game() {
        listOfObserver = new ArrayList<>();
    }


    public void registerObserver(Observer observer) {
        listOfObserver.add(observer);
    }

    public void startGame() {
        ...
        ...
        ...

        /* when something important happens */
        for (int i = 0; i < listOfObserver.size(); i++)
            listOfObserver.notify();

        ...
        ...
        ...
    }
}

然后，main()函数：

public class Main
{
    public static void main(String args[]) {
        Player player1 = new Player();
        Player player2 = new Player();
        Player player3 = new Player();
        Player player4 = new Player();

        Judge judge = new Judge();

        Game game = new Game();
        game.registerObserver(player1);
        game.registerObserver(player2);
        game.registerObserver(player3);
        game.registerObserver(player4);
        game.registerObserver(judge);

        game.startGame();
    }
}

一个类如何调用另一个类的方法，其中一个类不是另一个类的父类或子类？

3 个答案: