Java 扩展了替代方案

发布于 2024-12-12 09:36:53 字数 573 浏览 5 评论 0原文

我正在尝试制作我们大学课程管理系统的模型（针对课程）。我偶然发现了extends的一个小限制，即某个类不可能扩展两个类。模型如下：

                     Professor
                    /                  
             Staff
          /          \                       
    Person            Tutor            
           \         /      
             Student

因此，我得到了员工和学生扩展人员和教授扩展员工。现在我和班级导师有一个小困境，他基本上是一个学生（有学生ID），但在某种意义上是大学员工（举办小组讲座，负责某个项目等）。由于我不能使用两个扩展，那么还有什么其他替代方案，如果可能的话，有人可以用 implements 给出一个非常简单的示例吗？我已经看到了它的接口示例，但我不太确定如何在我的程序中使用它，因为 Student 不是接口？

原文

I'm trying to make a model of our universities Course management system (for the course). I stumbled upon a small limitation of extends, that is, it's impossible for a certain class to extend two classes. Here's the model:

                     Professor
                    /                  
             Staff
          /          \                       
    Person            Tutor            
           \         /      
             Student

So with that I get Staff and Student extending Person and Professor extending Staff. Now I have a small dilemma with class Tutor, who is basically a student (has studentID), but is in a sense University employee (holds Group lectures, responsible for a certain project, etc). Since I can't use two extends, what are other alternatives, and if possible could someone give a very simple example with implements? I've seen an example of interface of it, but I'm not exactly sure as how can I use it in my program, since Student is not an interface?

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墨小墨 2024-12-19 09:36:53

不要使用继承，使用组合：每个人都是一个人，但都有一个或多个角色：学生、导师、教授、职员。

或者可以选择在教职员工和学生之间进行划分，并允许他们担任角色。然后，角色决定他们可以做什么或不能做什么。

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黯然 2024-12-19 09:36:53

你可以做这样的事情。

interface Person { ... }

interface Staff extends Person { ... }

interface Student extends Person { ... }

class Tutor implements Staff, Student { ... }

class Professor implements Staff { ... }

不幸的是，您不能将逻辑（即字段或非抽象方法）同时放入 Staff 和 Student 中，因为它们都需要是类，并且是 Java 类不能扩展两个类。

您可以将 Student 或 Staff （不是两者）设置为抽象类，从而允许您将逻辑放入其中。不过，这有点不优雅，因为没有概念上的理由说明为什么一个应该是抽象类，而一个应该是接口。理想情况下，它们都应该是抽象类，但为此您需要切换到具有 MI 的语言。

interface Person { ... }

interface Staff extends Person { ... }

abstract class Student implements Person {
    long studentID;
    ...
}

class Tutor extends Student implements Staff { ... }

class Professor implements Staff { ... }

You can do something like this.

interface Person { ... }

interface Staff extends Person { ... }

interface Student extends Person { ... }

class Tutor implements Staff, Student { ... }

class Professor implements Staff { ... }

Unfortunately, you can't put logic (i.e., fields or non-abstract methods) in both Staff and Student because they would both need to be classes, and a Java class cannot extend two classes.

You could make Student or Staff (not both) an abstract class, allowing you to put logic in it. It would be kind of inelegant, though, since there's no conceptual reason why one should be an abstract class while one should be an interface. Ideally they should both be abstract classes, but for that you'd need to switch to a language with MI.

interface Person { ... }

interface Staff extends Person { ... }

abstract class Student implements Person {
    long studentID;
    ...
}

class Tutor extends Student implements Staff { ... }

class Professor implements Staff { ... }

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