Help me in solving OPJA92 problem

help
,
1

My issue

help

My code

// Base class Student
class Student {
    String studentName;

    Student(String studentName) {
        this.studentName = studentName;
    }

    public void displayDetails() {
        System.out.println("Student Name: " + studentName);
    }
}

// Derived class Graduate
class Graduate extends Student {
    int graduationYear;

    Graduate(String studentName, int graduationYear) {
        super(studentName);
        this.graduationYear = graduationYear;
    }

    @Override
    public void displayDetails() {
        super.displayDetails();
        System.out.println("Graduation Year: " + graduationYear);
    }
}

// Derived class Postgraduate
class Postgraduate extends Graduate {
    String thesisTopic;

    Postgraduate(String studentName, int graduationYear, String thesisTopic) {
        super(studentName, graduationYear);
        this.thesisTopic = thesisTopic;
    }

    @Override
    public void displayDetails() {
        super.displayDetails();
        System.out.println("Thesis Topic: " + thesisTopic);
    }
}

Learning course: Advanced Java programming
Problem Link: Student and Postgraduate in Advanced Java programming