Access elements of arraylist of arraylist of arraylist?

Question

I am new to Java, and I am currently using BlueJ for a project. I am having troubles accessing the objects inside an ArrayList of an ArrayList of such objects. Say I have a Student object:

public class Student
{
 private String homeAddress;
 private String monthBorn;
 private String yearBorn;
 private int;

 public Student(String homeAddress, String monthBorn, String yearBorn,  
 int finalGrade)
 {
   this.homeAddress = homeAddress;
   this.monthBorn = monthBorn;
   this.yearBorn = yearBorn;
   this.finalGrade = finalGrade;
  }
}

And then methods to get address, month, year and grade. Then I have a class Class, which is an ArralyList of Student objects:

    public class Classroom
    {
      private String classroom;
      private ArrayList<Student> listOfStudents;

     public Classroom (String classroom)
     {
      this.classroom = classroom;
      listOfStudents = new ArrayList<Student>();
     }
   }

And this class includes methods to add Student objects, to list all the students in the class (listAllStudentsInClassroom) which returns an ArrayList of Student, to find the Student with the highest grade in the class (getHighestGradeStudent), and to a list of students with grades higher than a certain amount. Finally, the class School, which is an ArrayList of Classroom:

public class School
{
 private ArrayList<Classroom> school;

 public School()
 {
  school = new ArrayList<Classroom>();
  }
}

This includes methods to add a class object, and it should include methods to return the Student with the highest grade ever and a list of students from all classes with grades higher than a certain one. However, I can only get the methods to iterate through only the first class added! Here is the code for getHighestGradeStudentEver so far:

    public Student getHighestGradeStudentEver ()
    {
      Student s = school.get(0).getHighestGradeStudent();
      int highestGrade =   school.get(0).listAllStudentsInClassroom().get(0).getFinalGrade();
      for(int i =1; i< school.size(); i++){
        int highestGrade = school.get(i).listAllStudentsInClassroom().get(i).getFinalGrade();
       if(value > (highestValue)){
           highestValue = value;
           s = school.get(i).getHighestGradeStudent();
           }
         }
      return s;
     }

This only returns the student with the highest grade from the first classroom object added to School. What am I doing wrong? Sorry for the long question, I tried to be as clear as possible!

Answer 1

If you can already get the highest graded student in a class, you can get that for all the classes, and find the highest grade out of all of those.

// find the highest grade in each class
ArrayList<Student> highestInEachClass = new ArrayList<>();
for (Classroom classroom : school) {
    highestInEachClass.add(classroom.getHighestGradeStudent());
}

// find the highest grade overall
Student highestGradeStudent = highestInEachClass.get(0);
for (Student student : highestInEachClass) {
    if (highestGradeStudent.getFinalGrade() < student.getFinalGrade()) {
        highestGradeStudent = student;
    }
}
return highestGradeStudent;

Alternatively, use Stream:

return school.stream().flatMap(x -> x.getListOfStudents().stream())
                      .sorted(Comparator.comparing(Student::getFinalGrade).reversed())
                      .findFirst().orElse(null);