Comparator before and after sorting

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
class Student {
int a;
String b,c;
public Student(int a, String b, String c) {
this.a = a;
this.b = b;
this.c = c;
}
public String toString() {
return this.a + "--"+ this.b + "--" + this.c + "--";
}
}
class Teacher implements Comparator<Student> {
@Override
public int compare(Student object1, Student object2) {
return object1.b.compareTo(object2.c);
}
}
class ComparatorBeforeandAfterSorting {
public static void main(String[] args) {
ArrayList<Student> a1 = new ArrayList<Student>();
a1.add(new Student(1,"A","Z"));
a1.add(new Student(1,"F","M"));
a1.add(new Student(1,"R","Q"));
a1.add(new Student(1,"E","U"));
a1.add(new Student(1,"C","U"));
System.out.println("before sorting");
for(int i=0;i<a1.size();i++) {
System.out.println(a1.get(i));
}
Collections.sort(a1, new Teacher());
System.out.println("after sorting");
for (int i = 0; i < a1.size(); i++) {
System.out.println(a1.get(i));
}
}
}