How to set time on a Date object to be zero (00/00/00)

Calendar calendar = Calendar.getInstance();
calendar.setTi开发者_如何学运维meInMillis(0);

This sets it to the deafult value. How do I set it to zero?

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You can zero-out what value you want using the set method. For example:

calendar.set(Calendar.HOUR, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);

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(00/00/00) is not a valid date; the API will not produce this value.

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You should probably be aware of what setTimeInMillis() expects:

public void setTimeInMillis(long millis)

Sets this Calendar's current time from the given long value.

Parameters:
millis - the new time in UTC milliseconds from the epoch.

The epoch is defined as:

An instant in time can be represented by a millisecond value that is an offset from the Epoch, January 1, 1970 00:00:00.000 GMT (Gregorian).