java基础

1. arraylist soring

1) Collections.sort(al);

2) 

    public void stackSorting(String stk) {
        // write your code here
        ArrayList aa = new ArrayList();

        aa.sort(new Comparator(){
            @Override
            public int compare(int arg0, int arg1){
                return aa.get(arg0).compareTo(aa.get(arg1));
            }
        });

    }
}
class SortByAge implements Comparator {
    public int compare(Object o1, Object o2) {
        Student s1 = (Student) o1;
        Student s2 = (Student) o2;
        return s1.getAge().compareTo(s2.getAge());
//          if (s1.getAge() > s2.getAge())
//           return 1;
//          return -1;
    }
}