使用Collection.sort对链表进行排序

Question

import java.util.*;

class MyComp<Subject> implements Comparator<Subject> {
    public int compare(Subject s1, Subject s2) {
        return s1.year - s2.year;
    }
}

public class Subject {
    String subjectID;
    int sem;
    String dept;
    public int year;
    String subjectName;
    int theortical;
    int practical;
    int tutorial;
}

我在编译cannot find symbol s1.year时遇到问题。 s2.year也是如此。