static List<Integer> intList = Arrays.asList(2,5,7, 3, 1);

       public static void main(String[] args) { 

           System.out.println("before sort:");

             PrintUtil.showList(intList);

             System.out.println("=========================");

             Collections.sort(intList,new Comparator<Integer>() {

                 public int compare(Integer o1, Integer o2) {

                     // 返回值为int类型，大于0表示正序，小于0表示逆序

                     System.out.println("o2-o1:"+(o2-o1)+"========o2="+o2+"o1="+o1);

                     if(o2>o1){

                         return -1;

                     }else{

                         return 1;

                     }

                 }

             });

             System.out.println("after sort:");

             PrintUtil.showList(intList);

     }