如何在 java 中为 object 赋予多个角色？

Question

the student and teacher class inherited from person class, because inheritance is not flexible the object will either be one of the two. to solve this i added an abstract class Role and make association between person and role and student and teacher inherits from Role class so that an instance can has a role of both student and teacher.The question is to make instance of the Teacher class can also be a student or a student also teaches how to test in the main class?

public class Person {

    private int ssn;
    private String name;
    private List<PersonRole> roles;

    public Person(int ssn, String name) {
        this.ssn = ssn;
        this.name = name;
        roles = new ArrayList<PersonRole>();
    }

    public int getSsn() {
        return ssn;
    }

    public String getName() {
        return name;
    }
   }

/////////////// PersonRole /////////////////

public abstract class PersonRole {
    private List<PersonRole> learning;
    private List<PersonRole> teaching;

    public PersonRole(List<PersonRole> learning, List<PersonRole> teaching) {
        this.learning = learning;
        this.teaching = teaching;
    }
     public List<PersonRole> getLearning() {
        return learning;
    }
    public List<PersonRole> getTeaching() {
        return teaching;
    }
    
    public void addAsStudent(PersonRole p) {
        learning.add(p);
    }
    public void addAsTeacher(PersonRole p) {
        learning.add(p);
    }
    }

/////////////  Teacher //////////////

public class Teacher extends PersonRole {

    private String faultyName;
    private int yearsOfExperence;

    public Teacher(String faultyName, int yearsOfExperence) {
        super();
        this.faultyName = faultyName;
        this.yearsOfExperence = yearsOfExperence;
    }

    public String getFaultyName() {
        return faultyName;
    }

    public int getYearsOfExperence() {
        return yearsOfExperence;
    }

}

///////////  Student  ////////////////

public class Student extends PersonRole {

    private String collegeName;
    private String major;

    public Student(String collegeName, String major) {
        super();
        this.collegeName = collegeName;
        this.major = major;
    }

    public String getCollegeName() {
        return collegeName;
    }

    public String getMajor() {
        return major;
    }

}


////// Main ///////////////

public class Main {

    public static void main(String[] args) {
        PersonRole p1 = new Student("univ of Michigan", "CS");
        PersonRole p3 = new Student("Iowa state univ", "managemnt");
        PersonRole p2 = new Teacher("computer science", 3);
        PersonRole p4 = new Teacher("Management", 2);

        Person person = new Person(1042327867, "Mike Rose");

        person.addRole(p1);
        person.addRole(p2);
        person.addRole(p3);
        person.addRole(p4);

        for (PersonRole c: roles) {
            System.out.println(c);
        }
    }
} 

Answer 1

I would test it exactly as you would but the hierarchy of inheritance looks good. Why not give PersonRole a constructor and attributes so that the children can use super() in their constructors and reuse some code?

Answer 2

Try this to print your roles:

List<PersonRole> roles = person.getRole();
for(PersonRole role: roles) {
    System.out.println(role);
}

Then add a toString method in the Student and Teacher classes:

public String toString() {
    return "Student {" + "collegeName=" + collegeName + ", major=" + major + '}';
}

public String toString() {
    return "Teacher {" + "faultyName=" + faultyName + ", yearsOfExperence=" + yearsOfExperence + '}';
}

The result will be this:

Student {collegeName=maharashi univ, major=compro}
Teacher {faultyName=computer science, yearsOfExperence=3}
Student {collegeName=Iowa state univ, major=managemnt}
Teacher {faultyName=Management, yearsOfExperence=2}