Question

我目前在用Code实现三元关联时遇到了一些麻烦。我得到二进制的但我不确定三元协会。

这是大学中的典型场景。

讲师可以为一个或多个学生教授一门学科
学生只能由一位讲师讲授一门学科
讲师只能教一个学生一个学科

这三个类之间存在三元关联。

下面的UML类图中显示的这三个类之间的关系以及多重性都存在

我已经在互联网上阅读了有关这方面的不同资料，找不到解决方法

如何实现这三个类之间的关联？要么，通常，有什么方法可以实现类之间的关联（在Java中）？

Answer 1

一如既往，这取决于。

实现关联类的通常方法是使用关联数组。在您的示例中，您将（最终）组合使用Lecturer / Subject来访问Student的列表。如果您的要求不同，则可以例如在提供Subject时返回Student / Teacher的列表。

使用数据库时，表Lecturer中的主键为Subject / Student / Teaching。这样可以像上面提到的那样进行单独选择。

我的帽子里有些伪代码：

class Teaching {
  private Hash lectRef; // assoc. array 

  public void addTeaching(Lecturer lect, Student stud, Subject subj) {
    if lectRef[lect.hash] == None { lectRef[lect.hash] = []; }  
    // if none, default an empty array here
    // lect.hash is a unique hash code for the Lecturer object

    lectRef[lect.hash].append((stud, subj); 
    // tuple of student/subject referenced

    // if you need other fast results (e.g. subjects per student or the like) you need to hash them here too
  }

  public [(Stud, Subj)] studSubj (Lecturer lect) {
    return lectRef[lect.hash];  
    // returns the array of student/subject tuples
  }

  // add other result operations like subjects per student as needed
}

Answer 2

根据阿玛丹（Amadan）我正在准备答案

由于我是Java新手，语法可能不正确如果此解决方案有误，请纠正我

//Lecturer class
class Lecturer{
    private List<Klass> klassList; 

    public List<Klass> getKlasses(Klass klassList){
        retrun klassList;
    }

    public List<Klass> addKlasses(Klass klassList){
        this.klassList = klassList;
    }

    teachStudents(){
        klassList = getKlasses()

        for (int i = 0; i < klassList.size(); i++) {
            (klassList.get(i)).teachSubjectToStudent();
        }
    }
}

//Student class
class Student{
    private Klass klass;
    private List<Subject> learnedSubjectList; 

    public void learn(Subject subject){
        learnedSubjectList.add(subject);
    }
}

//Subject class
class Subject{
    private Klass klass;
}

//Klass class
class Klass{
    private Lecturer lecturer;
    private Student student;
    private Subject subject;

    Klass(Lecturer lecturer,Student student,Subject subject){
        private this.lecturer = lecturer;
        private this.student  = student;
        private this.subject  = subject;
    }

    //implimentation of how subject was teach to a student
    public void teachSubjectToStudent(){
        this.student.learn(subject)
    }
}

//this class is use for code execution
public class TestA {
    public static void main(String[] args) {
        Lecturer lecturer = new Lecturer();
        Subject subject   = new Subject();

        Student student1   = new Student();
        Student student2   = new Student();
        Student student3   = new Student();

        Klass klass1 = new Klass(lecturer,student1,subject);
        Klass klass2 = new Klass(lecturer,student2,subject);
        Klass klass3 = new Klass(lecturer,student3,subject);

        List<Klass> list = new ArrayList<Klass>();
        list.add(klass1);
        list.add(klass2);
        list.add(klass3);

        //create association link between lecturer class and klass class list
        lecturer.addKlasses(list);
    }
}

Answer 3

通常，您会自行将关联本身建模为实体（不能称为其类Class，因为java.lang.Class已经采用了该类；通常人们将此类命名为{ {1}}，很明显它指的是；您也可以使用Klass。然后，您只有Teaching和Klass，Teacher和Klass，Subject和Klass之间的二进制关联。在这种情况下，Student和Teacher根本没有关联，除非通过与Student的参与（与其他对相似）间接地关联。

Java代码中的隐式UML三元关联

3 个答案: