Java Implementing interface Comparable, comparing manually entered data with generated data

Question

Question: How to I directly compare manually entered student infomation (shown below = 'Elise') with other student Aggergate marks, then sort the data with the largest 'Aggergate' number at the top of the output file.

 public class Student2 implements Comparable<Student2> {

@Override
   public int compareTo(Student2 o) {
        return Double.valueOf(this.aggerate()).compareTo(Double.valueOf(o.aggerate()));
     if (result > 0) {
         return 1;
         } else if (result < 0) {
         return -1;
         } else {
         return 0;
         }
         }


public static void main(String... args) {
Set<Student2> Stu = new TreeSet<>(
                    Comparator.comparing(Student2::aggregate).reversed()
                              .andThen(Student2::getId));
    Stu.add(new Student2(25321, "Elsie", 51.5, 45.6, 48.5, "3rd", "Proceed To Stage 2"));
    Stu.stream().forEach((c) -> {
        System.out.println(c);
    });
}

public double aggerate() {
    DecimalFormat decFormat = new DecimalFormat("#.#");
    double aggerateMarks = Double.valueOf(decFormat.format((IR101Grades +  IR102Grades) / 2));
    aggerateMarks = Math.round(aggerateMarks * 100.0) / 100.0;
    return aggerateMarks;

}
public String toString() {
    return "\n" + studentID + " |" + studentName + "\n" + "IR101: " + IR101Grades + " | " + "IR102: " + IR102Grades + " |"
            + " Aggregate Mark: " + aggerate() + "\n" + "Class: " + setGrade() + " | " + "Outcome: " + setClass()
            + "\n" + "\n" + "-----------------------------------------------------" + "\n" + "\n";
}

Answer 1

To create a TreeSet which reverse sorts by aggregate you can do

Set<Student2> Stu = new TreeSet<>(
                        Comparator.comparing(Student2::aggregate).reversed()
                                  .andThen(Student2::getId));

This way your tree will be in reverse order.

Note: just in case two students have the same aggregate, the getID should ensure they are never considered a duplicate