将日历日期设置为当前日期

Question

我有一个变量timeInMills，它是3天前的值，我想将其日期重置为当前日期，但是时间应该仍然是。

Calendar calNow = Calendar.getInstance();
Calendar calSets = (Calendar)calNow.clone();

calSets.setTimeInMillis(TIME_IN_MILL); //set datetime from timeInMillis
//Reset the date to current Date.

该怎么做？

Answer 1

像这样，在更改实例之前获取所需的属性：

i

Answer 2

您可以通过调用Calendar来重置setTimeInMillis(System.currentTimeMillis())：

TimeZone.setDefault(TimeZone.getTimeZone("UTC")); // Just for testing

final long TIME_IN_MILL = 1563204600000L; // 2019-07-15 15:30 UTC

Calendar cal = Calendar.getInstance();
cal.setTimeInMillis(TIME_IN_MILL);
int hour = cal.get(Calendar.HOUR_OF_DAY);
int minute = cal.get(Calendar.MINUTE);
cal.setTimeInMillis(System.currentTimeMillis()); // Reset
cal.set(Calendar.HOUR_OF_DAY, hour);
cal.set(Calendar.MINUTE, minute);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);

System.out.println(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(cal.getTime()));

代码显示2019-07-18 15:30:00.000，它是从TIME_IN_MILL值开始的今天的日期和一天中的时间。

如果您不想依赖System.currentTimeMillis()，只需从Calendar对象获取值，

Calendar cal = Calendar.getInstance();
long now = cal.getTimeInMillis();

cal.setTimeInMillis(TIME_IN_MILL);
int hour = cal.get(Calendar.HOUR_OF_DAY);
int minute = cal.get(Calendar.MINUTE);

cal.setTimeInMillis(now);
cal.set(Calendar.HOUR_OF_DAY, hour);
cal.set(Calendar.MINUTE, minute);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);