Check this out.
The following should help:
//import Exceptions.*;
import Exceptions.TooManyGradesException;
import Exceptions.GradeOutOfBoundException;
import Exceptions.GohstStudentException;
import Exceptions.NoGradesException;
It's pretty late here, I'll hit the bed. But the above should help you to move forward.
Good luck!
Update
I've got a bit of time now. :)
Apply the above change to the Classroom.java file. Also, add the following import:
import java.util.Arrays;
There's a problem with the NoGradesException.java file as well. Do not throw an exception there, instead call the constructor of the base class:
super("this student doesn't have a grade");
Packages...
I'm not a Java developer. But it seems like working with packages makes life complicated in OnlineGDB. If you use packages (apply the above fixes first), the compiler will be unable to initialize the Main class as it won't find all the dependencies (the Exceptions package). I don't know how to fix it. Most online resources talk about fixing your project, but we don't really have a project file here. Maybe it needs a compilation flag?
Anyway, a simple workaround is not to use packages when using OnlineGDB.
After this (and removing all the import Exceptions.?????) your code should run.