这是协会或聚集的情况下？ [英] is this a case of association or aggregation?

问题描述

我已经发现了大约学生一组课程如何注册一个Java的例子：

I have found a Java example about how students register in a set of courses:

学生-----需要------课程

Student-----takes------Courses

和在本例中被定义为协会，但为什么它不能是聚合？对于我所看到的每一个类都可以独立存在。如何区分这两个？

and in the example is defined as Association, but why it cannot be Aggregation? for what I see each class could exist independently. How do differentiate both?

在我处理的一个学生有课程作为属性的数组，当然有其内生也是一个数组的架构上面的例子;所以在这种情况下，是因为联想两者是相关的，和聚集，因为一个被包含在里面其他？

In the above example I am dealing with the schema that a Student has an array of Courses as attribute, and Course has an array of Students within it also; so in that case is association because both of them are related, and aggregation because one is contained inside the other?

推荐答案

这是不是集合，因为课程是不是学生的集合，一个学生是不是课程的集合。这是一个简单许多一对多关联。我也看到了这一点与封装所需的方法和数据，让学生报名参加课程的关联类者登记为蓝本。聚合的一个例子是如何在一个体商店应用存在一辆车。该车拥有可以独立存在可拆卸的部件（轮胎，发动机，底盘等），但它会知道哪些部件在一个特定的汽车仍存在有用的。

This is not aggregation since a course is not a collection of students and a student is not a collection of courses. This is a simple many-to-many association. I have also seen this modeled with an association class "enrolls" which encapsulates the methods and data necessary to allow a student to sign up for a course. An example of aggregation would be how a car exists in a body shop application. The car has removable parts (tires, engine, chassis, etc.) which can exist independently but it would be useful to know which parts still exist on a particular car.

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