Trying to make sense of the following output:
public class CommunicationComparator implements Comparator<Communication> {
@Override
public int compare(Communication comm1, Communication comm2) {
long t1 = comm1.getDate().getTime();
long t2 = comm2.getDate().getTime();
return (int) (t2 - t1);
}
}
The method getDate() returns a java.sql.Timestamp.
Here is the output before the sort:
for (Communication n : retVal) {
System.out.println(n.getDate().toString());
}
2012-10-03 10:02:02.0
2012-10-07 03:02:01.0
2012-10-08 13:02:02.0
2012-10-09 03:02:00.0
2012-11-26 10:02:05.0
2012-11-28 11:28:11.0
2012-12-03 12:03:01.0
2012-12-06 15:03:01.0
2012-12-13 14:03:00.0
2012-12-28 11:03:00.0
2012-12-28 13:49:21.0
And after:
Collections.sort(retVal, new CommunicationsComparator());
2012-12-13 14:03:00.0
2012-12-06 15:03:01.0
2012-12-03 12:03:01.0
2012-11-28 11:28:11.0
2012-10-09 03:02:00.0
2012-10-08 13:02:02.0
2012-11-26 10:02:05.0
2012-10-07 03:02:01.0
2012-10-03 10:02:02.0
2012-12-28 13:49:21.0
2012-12-28 11:03:00.0
Any ideas why the bottom two objects might not be sorted correctly? I am using the MySQL JDBC implementation of this Timestamp.
The difference between the last 2 dates and earlier dates will overflow integer.
Perhaps a better solution would be to compare the values, rather than subtract them.
long t1 = comm1.getDate().getTime();
long t2 = comm2.getDate().getTime();
if(t2 > t1)
return 1;
else if(t1 > t2)
return -1;
else
return 0;
If the difference is bigger than about 25 days, an overflow occurs. (An int cannot represent a bigger time difference in milliseconds than about 25 days). This will make the comparison incorrect.
This can be solved by changing the return statement into:
return Long.signum(t2 - t1);
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