Difference in hours of two Calendar objects

问题:

I have two Calendar objects, and I want to check what is the difference between them, in hours.

Here is the first Calendar

Calendar c1 = Calendar.getInstance();

And the second Calendar

Calendar c2 = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd HH:mm:ss z yyyy", Locale.ENGLISH);
c2.setTime(sdf.parse("Sun Feb 22 20:00:00 CET 2015"));

Now lets say that c1.getTime() is: Fri Feb 20 20:00:00 CET 2015 and c2.getTime() is Sun Feb 22 20:00:00 CET 2015.

So is there any code that would return the difference between first and second Calendar in hours? In my case it should return 48.

回答1:

You can try the following:

long seconds = (c2.getTimeInMillis() - c1.getTimeInMillis()) / 1000;
int hours = (int) (seconds / 3600);

Or using the Joda-Time API's Period class, you can use the constructor public Period(long startInstant, long endInstant) and retrieve the hours field:

Period period = new Period(c1.getTimeInMillis(), c2.getTimeInMillis());
int hours = period.getHours();

回答2:

In Java 8 you could do

long hours = ChronoUnit.HOURS.between(c1.toInstant(), c2.toInstant());