Help me in solving OPJA92 problem

help
,
1

My issue

Failed on a hidden test case please help me to slove this program

My code

class Student {
    String studentName;

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

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

class Graduate extends Student {
    int graduationYear;

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

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

class Postgraduate extends Graduate {
    String thesisTopic;

    public 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);
    }
}

public class Main {
    public static void main(String[] args) {
        Student student = new Student("Alice");
        student.displayDetails();
        System.out.println();

        Graduate graduate = new Graduate("Bob", 2025);
        graduate.displayDetails();
        System.out.println();

        Postgraduate postgraduate = new Postgraduate("Charlie", 2023, "Machine Learning");
        postgraduate.displayDetails();
    }
}

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