class Foo implements Comparable<Foo>{

    @Override

    public int compareTo(ClientPortalButton o) {

        return this.i.compareTo(o.getI());

    }

}

public static void main(String[] args) {

        List<Students> students = new ArrayList<Students>();

        students.add(new Students(23, 100));

        students.add(new Students(27, 98));

        students.add(new Students(29, 99));

        students.add(new Students(29, 98));

        students.add(new Students(22, 89));

        Collections.sort(students, new Comparator<Students>() {  

            @Override

            public int compare(Students o1, Students o2) {

                int i = o1.getScore() - o2.getScore();

                if(i == 0){

                    return o1.getAge() - o2.getAge();

                }

                return i;

            }

        });

        for(Students stu : students){

            System.out.println("score:" + stu.getScore() + ":age" + stu.getAge());

        }

}