这段在学生类中重写的compareTo中的this代表什么？如果o是代表传入的学生对象，那么return中的那个this又代表什么呢？

student中重写的conpareTo:

@Override

public int compareTo(student o) {

// TODO 自动生成的方法存根

return this.id.compareTo(o.id);

}

要求排序的student泛型的list：

List<student> studentlist = new ArrayList<student>();

Random r1 = new Random();

studentlist.add(new student(100000000 + "", "A"));

studentlist.add(new student(r1.nextInt(1000) + "", "MING"));

studentlist.add(new student(r1.nextInt(1000) + "", "Hong"));

studentlist.add(new student(r1.nextInt(1000) + "", "Lv"));

System.out.println("------排序前------");

for (student student : studentlist) {

System.out.println("学生" + student.id + ":" + student.name);

}

Collections.sort(studentlist);

System.out.println("------排序后------");

for (student student : studentlist) {

System.out.println("学生" + student.id + ":" + student.name);

}