java - 如何在java中舍入一毫秒？

Question

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舍入。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方程来计算这个？

Answer 1

您可以通过像这样利用下降来消除所有重复的行：

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();
}

Answer 2

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);
        default:
            calendar.set(Calendar.MILLISECOND, 0);
    }
    return calendar.getTimeInMillis();
}

注意里面没有breakorreturn语句switch。这会导致switch块中的语句落入下一个case标签。

本教程中对此进行了介绍。

Answer 3

还calender.set(Calendar.MILLISECOND, 0)不够吗？

另一种方法是：

return date.getTime() / 1000 * 1000;

Answer 4

您可以在 switch 语句中利用“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();

}