如何在java中循环一毫秒？

Java代码

public static long round(long millis , TimeUnit unit){
    Calendar calendar = Calendar.getInstance();
    switch(unit){
        case DAYS:
            calendar.set(Calendar.MILLISECOND, 0);
            calendar.set(Calendar.SECOND,0);
            calendar.set(Calendar.MINUTE, 0);
            calendar.set(Calendar.HOUR, 0);
            return calendar.getTimeInMillis();
        case HOURS:
            calendar.set(Calendar.MILLISECOND, 0);
            calendar.set(Calendar.SECOND, 0);
            calendar.set(Calendar.MINUTE, 0);
            return calendar.getTimeInMillis();
        case MINUTES:
            calendar.set(Calendar.MILLISECOND , 0);
            calendar.set(Calendar.SECOND, 0);
            return calendar.getTimeInMillis();
        case SECONDS:
            calendar.set(Calendar.MILLISECOND, 0);
            return calendar.getTimeInMillis();
        case MILLISECONDS:
        default:
            calendar.set(Calendar.MILLISECOND, 0);
            return  calendar.getTimeInMillis();
    }
}

目前，我正在使用此代码对毫秒值进行四舍五入。在这种方法中，代码的冗余是一个大问题

---

有没有更好的解决方案或数学公式来计算这一点？

您可以通过如下方式利用下降法消除所有重复行：

public static long round(long millis , TimeUnit unit){
    Calendar calendar = Calendar.getInstance();
    switch(unit){
        case DAYS:
            calendar.set(Calendar.HOUR, 0);
        case HOURS:
            calendar.set(Calendar.MINUTE, 0);
        case MINUTES:
            calendar.set(Calendar.SECOND, 0);
        case SECONDS:
        case MILLISECONDS:
        default:
            calendar.set(Calendar.MILLISECOND, 0);
    }
    return calendar.getTimeInMillis();
}

注意

开关中没有
break
或
return
语句。这会导致
开关
块中的语句转到下一个
案例
标签

这在中有介绍。
不仅仅是
日历。设置（Calendar.millis秒，0）
就足够了吗

另一种方法是：

return date.getTime() / 1000 * 1000;

您可以利用switch语句中的“fallthrough”：

public static long round(long millis , TimeUnit unit){
    Calendar calendar = Calendar.getInstance();
    switch(unit){
        case DAYS:
            calendar.set(Calendar.HOUR, 0);
        case HOURS:
            calendar.set(Calendar.MINUTE, 0);
        case MINUTES:
            calendar.set(Calendar.SECOND, 0);
        case SECONDS:
            calendar.set(Calendar.MILLISECOND, 0);
    }
    return  calendar.getTimeInMillis();

}

public static long round(long millis , TimeUnit unit){
    Calendar calendar = Calendar.getInstance();
    switch(unit){
        case DAYS:
            calendar.set(Calendar.HOUR, 0);
        case HOURS:
            calendar.set(Calendar.MINUTE, 0);
        case MINUTES:
            calendar.set(Calendar.SECOND, 0);
        case SECONDS:
            calendar.set(Calendar.MILLISECOND, 0);
    }
    return  calendar.getTimeInMillis();

}