如何通过对象传递在另一个泛型类中访问类的属性？

Question

In my code, Generic class Public will receive a generic object in check() method. These generic objects might be from JuniorInstructor class or SeniorInstructor class.I wanna access the properties of JuniorInstructor class or SeniorInstructor class. I tried with below implementation and it works. But, Is there any better way to do this?

   class JuniorInstructor extends Instructor {

    public JuniorInstructor(String id, String name) {
        super(id, name);

    }

}

class Public<T> {
    T object;
    JuniorInstructor j1;
    SeniorInstructor s1;

    public void check(T object) {

        this.object = object;
        if (object instanceof SeniorInstructor) {
            s1 = (SeniorInstructor) object;
            System.out.println("name: " + s1.name + "\tid: " + s1.id);
        } else {
            j1 = (JuniorInstructor) object;
            System.out.println("name: " + j1.name + "\tid: " + j1.id);
        }
    }// check
}
public static void main(String[] args) {
        SeniorInstructor s1 = new SeniorInstructor("120", "Ashik");
        JuniorInstructor j1 = new JuniorInstructor("677", "Tareq");
        Public p = new Public();

        p.check(j1);

    }

Answer 1

You can further qualify T :

class Public<T extends Instructor>

And simply make sure all the methods you need to access are defined on Instructor . You'll then be able to call them directly in Public .

[Edit] @JBNizet has an excellent point in comments that Public doesn't really need to be generics if Instructor and its subclasses are all it needs to handle.

Answer 2

You can declare the Public class like

class Public<T extends Instructor> {
      ...
   }

in this way you can avoid to check for instance type, as long as you need to access to 'Instructor' property.

Hope this help

Answer 3

I think might want to use polymorphism instead of generics .

Create 2 overloaded versions of check method:

• one that accepts a JuniorInstructor
• one that accepts a SeniorInstructor

In this way, there is no need to use instanceOf or casting objects to a given type.

class Public {
    JuniorInstructor j1;
    SeniorInstructor s1;

    public void check(SeniorInstructor object) {
        s1 = object;
        System.out.println("name: " + s1.getName() + "\tid: " + s1.getId());
    }

    public void check(JuniorInstructor object) {
        j1 = object;
        System.out.println("name: " + j1.getName() + "\tid: " + j1.getId());
    }
}

Answer 4

As Ward mentioned,

One of the benefits of generics is that you can write generic code, without the need for using instanceof and casting etc...

You can modify the Public class as below :

class Public<T extends Instructor> {
   T instructor;

   public void check(T object) {
       this.instructor = object;
       System.out.println("name: " + this.instructor.name + "\tid: " + this.instructor.id);
   }
}

Answer 5

public class Instructor {

private String id;
private String name;

public Instructor(String id, String name) {
        this.id= id; this.name= name;
}

//getters and setters
 }

Then a class public :

class Public<T extends Instructor> {
T object;

public void check(T object) {
        System.out.println("name: " + object.getName() + "\tid: " + object.getId());
}
}

However, if your class has only 1 method using this T as parameter, you can modify it to:

class Public {

public <T extends Instructor> void check(T object) {
        System.out.println("name: " + object.getName() + "\tid: " + object.getId());
}
 }

Or since usage of generics is not clear here, we can simply use:

class Public {

public  void check(Instructor object) {
        System.out.println("name: " + object.getName() + "\tid: " + object.getId());
}
 }

And in main:

 public static void main(String[] args) {
    Public obj= new Public();
    obj.check(new JuniorInstructor("1","Payal"));
}