Java Calendar奇怪的行为

Question

I'm trying to use a java calendar on which I'm trying to compute the next 7 days after a specific date as following:

java.sql.Timestamp lastDate= Timestamp.valueOf("2015-12-28 00:00:00.0");

I have a batch job that runs and updates that date to occur weekly. The way I did it is as follows :

Calendar calNextDate = Calendar.getInstance();
calNextDate.setTime(new java.util.Date(lastDate.getTime()));

calNextDate.add(Calendar.DAY_OF_MONTH, 7);

System.out.println(new Timestamp(calNextDate.getTime().getTime()));

Output :

2016-01-04 00:00:00.0

but when I use the same function to compute for the year 2014 the date is:

2015-01-05 00:00:00.0

I have added 7 days on both the cases but in case of 2014, 1 day is off, why would that be?? thanks in advance.

Answer 1

Problem Not Reproducible

I do not see the problem.

Here is a re-creation of the code you described but did not post.

java.sql.Timestamp ts2013 = Timestamp.valueOf ( "2013-12-28 00:00:00.0" );
java.sql.Timestamp ts2014 = Timestamp.valueOf ( "2014-12-28 00:00:00.0" );
java.sql.Timestamp ts2015 = Timestamp.valueOf ( "2015-12-28 00:00:00.0" );

Calendar cal2013 = Calendar.getInstance ( );
cal2013.setTime ( new java.util.Date ( ts2013.getTime ( ) ) );
cal2013.add ( Calendar.DAY_OF_MONTH, 7 );
java.sql.Timestamp ts2013Plus = new Timestamp ( cal2013.getTime ( ).getTime ( ) );
System.out.println ( ts2013 + " + 7 = " + ts2013Plus );

Calendar cal2014 = Calendar.getInstance ( );
cal2014.setTime ( new java.util.Date ( ts2014.getTime ( ) ) );
cal2014.add ( Calendar.DAY_OF_MONTH, 7 );
java.sql.Timestamp ts2014Plus = new Timestamp ( cal2014.getTime ( ).getTime ( ) );
System.out.println ( ts2014 + " + 7 = " + ts2014Plus );

Calendar cal2015 = Calendar.getInstance ( );
cal2015.setTime ( new java.util.Date ( ts2015.getTime ( ) ) );
cal2015.add ( Calendar.DAY_OF_MONTH, 7 );
java.sql.Timestamp ts2015Plus = new Timestamp ( cal2015.getTime ( ).getTime ( ) );
System.out.println ( ts2015 + " + 7 = " + ts2015Plus );

When run, this code always get the 4th.

2013-12-28 00:00:00.0 + 7 = 2014-01-04 00:00:00.0
2014-12-28 00:00:00.0 + 7 = 2015-01-04 00:00:00.0
2015-12-28 00:00:00.0 + 7 = 2016-01-04 00:00:00.0

I conclude that your problem lies elsewhere.

java.time

I strongly suggest moving to use of the new java.time package in Java 8 and later. You can then entirely avoid the mess that is java.util.Date/.Calendar.

The java.sql.Timestamp class has been enhanced with new methods to easily convert to and from java.time types.

Eventually JDBC drivers will be updated to directly handle the java.time data types.