java中的list时间排序

最初设想使用：时间long型

    private void testTimes() throws InterruptedException{
        Calendar cal=Calendar.getInstance();
        cal.add(Calendar.DATE, 1);
        cal.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH), cal.get(Calendar.DAY_OF_MONTH), 0, 0, 0);
        Long time1=cal.getTimeInMillis();        Calendar ca2=Calendar.getInstance();
        ca2.add(Calendar.DATE, 1);
        ca2.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH), cal.get(Calendar.DAY_OF_MONTH), 0, 0, 0);        Long time2=ca2.getTimeInMillis();        System.out.println(time1+"--"+time2);
    }

发现整型可能不一致，即有时候一致，有时候不一致。

经测算发现，Collections提供了排序功能：

private void testSort(){
        List<Calendar> cals=new ArrayList<Calendar>();        Calendar cal3=Calendar.getInstance();
        cal3.add(Calendar.DATE, 2);
        cal3.set(cal3.get(Calendar.YEAR), cal3.get(Calendar.MONTH), cal3.get(Calendar.DAY_OF_MONTH), 0, 0, 0);        Calendar cal4=Calendar.getInstance();
        cal4.add(Calendar.DATE, 2);
        cal4.set(cal4.get(Calendar.YEAR), cal4.get(Calendar.MONTH), cal4.get(Calendar.DAY_OF_MONTH), 0, 0, 0);        Calendar cal1=Calendar.getInstance();
        cal1.add(Calendar.DATE, 2);
        cal1.set(cal1.get(Calendar.YEAR), cal1.get(Calendar.MONTH), cal1.get(Calendar.DAY_OF_MONTH), 0, 0, 2);        Calendar cal2=Calendar.getInstance();
        cal2.add(Calendar.DATE, 2);
        cal2.set(cal2.get(Calendar.YEAR), cal2.get(Calendar.MONTH), cal2.get(Calendar.DAY_OF_MONTH), 0, 0, 0);        cals.add(cal3);
        cals.add(cal4);
        cals.add(cal1);
        cals.add(cal2);        Calendar minTime=Collections.min(cals);        System.out.println(DateUtils.formatDate(Collections.min(cals).getTime(),"yyyy-MM-dd HH:mm:ss"));        for(int i=0;i<cals.size();i++){
            if(DateUtils.defaultFormatDate(minTime.getTime()).equals(DateUtils.defaultFormatDate(cals.get(i).getTime()))){
                System.out.println(DateUtils.formatDate(cals.get(i).getTime(),"yyyy-MM-dd HH:mm:ss"));
            }
        }
        /*        for(int i=0;i<cals.size();i++){
            System.out.println(DateUtils.formatDate(cals.get(i).getTime(),"yyyy-MM-dd HH:mm:ss"));
        }        Collections.sort(cals);        //排序后
        for(int i=0;i<cals.size();i++){
            System.out.println(DateUtils.formatDate(cals.get(i).getTime(),"yyyy-MM-dd HH:mm:ss"));
        }*/
    }