Gregorian calendar add/roll issue 1

[andrewbadera]

I have a 5-day Gantt-style timeline chart I'm working on with next/previous week buttons. On next/previous 7 days are added or subtracted from the current DAY_OF_YEAR value. It seems to scroll previous with no problems ... but at the end of September, it rolls back to the beginning of September.

The code:
public void actionPerformed(ActionEvent e) {
String actionCmd = e.getActionCommand();

int plusseven = 7;
int plusone = 1;
int negativeseven = -7;
int negativeone = -1;

if (actionCmd == "nextWeek&quot {
cal.add(Calendar.DAY_OF_YEAR, 7);
}
if (actionCmd == "prevWeek&quot {
cal.add(Calendar.DAY_OF_YEAR, negativeseven);
}

System.out.println("DAY_OF_YEAR: " + cal.get(Calendar.DAY_OF_YEAR));

paint(getGraphics());
}

The results of going forward:
Mon Aug 19 08:42:30 EDT 2002
Fri Aug 23 08:42:30 EDT 2002
Mon Aug 19 08:42:30 EDT 2002
Fri Aug 23 08:42:30 EDT 2002
DAY_OF_YEAR: 242
Mon Aug 26 08:42:30 EDT 2002
Fri Aug 30 08:42:30 EDT 2002
DAY_OF_YEAR: 249
Mon Sep 02 08:42:30 EDT 2002
Fri Sep 06 08:42:30 EDT 2002
DAY_OF_YEAR: 256
Mon Sep 09 08:42:30 EDT 2002
Fri Sep 13 08:42:30 EDT 2002
DAY_OF_YEAR: 263
Mon Sep 16 08:42:30 EDT 2002
Fri Sep 20 08:42:30 EDT 2002
DAY_OF_YEAR: 270
Mon Sep 23 08:42:30 EDT 2002
Fri Sep 27 08:42:30 EDT 2002
DAY_OF_YEAR: 277
Mon Sep 30 08:42:30 EDT 2002
Fri Sep 06 08:42:30 EDT 2002
Mon Sep 02 08:42:30 EDT 2002
Fri Sep 06 08:42:30 EDT 2002
DAY_OF_YEAR: 256

The results of going backwards:
Mon Sep 09 08:42:30 EDT 2002
Fri Sep 13 08:42:30 EDT 2002
DAY_OF_YEAR: 263
Mon Sep 16 08:42:30 EDT 2002
Fri Sep 20 08:42:30 EDT 2002
DAY_OF_YEAR: 270
Mon Sep 23 08:42:30 EDT 2002
Fri Sep 27 08:42:30 EDT 2002
DAY_OF_YEAR: 277
Mon Sep 30 08:42:30 EDT 2002
Fri Sep 06 08:42:30 EDT 2002
Mon Sep 02 08:42:30 EDT 2002
Fri Sep 06 08:42:30 EDT 2002
DAY_OF_YEAR: 256
Mon Sep 09 08:42:30 EDT 2002
Fri Sep 13 08:42:30 EDT 2002
Mon Sep 09 08:42:30 EDT 2002
Fri Sep 13 08:42:30 EDT 2002
Mon Sep 09 08:42:30 EDT 2002
Fri Sep 13 08:42:30 EDT 2002
DAY_OF_YEAR: 249
Mon Sep 02 08:42:30 EDT 2002
Fri Sep 06 08:42:30 EDT 2002
DAY_OF_YEAR: 242
Mon Aug 26 08:42:30 EDT 2002
Fri Aug 30 08:42:30 EDT 2002
DAY_OF_YEAR: 235
Mon Aug 19 08:42:30 EDT 2002
Fri Aug 23 08:42:30 EDT 2002
DAY_OF_YEAR: 228
Mon Aug 12 08:42:30 EDT 2002
Fri Aug 16 08:42:30 EDT 2002
DAY_OF_YEAR: 221
Mon Aug 05 08:42:30 EDT 2002
Fri Aug 09 08:42:30 EDT 2002
DAY_OF_YEAR: 214
Mon Jul 29 08:42:30 EDT 2002
Fri Jul 05 08:42:30 EDT 2002
DAY_OF_YEAR: 179
Mon Jun 24 08:42:30 EDT 2002
Fri Jun 28 08:42:30 EDT 2002
DAY_OF_YEAR: 172
Mon Jun 17 08:42:30 EDT 2002
Fri Jun 21 08:42:30 EDT 2002
DAY_OF_YEAR: 165
Mon Jun 10 08:42:30 EDT 2002
Fri Jun 14 08:42:30 EDT 2002
DAY_OF_YEAR: 158
Mon Jun 03 08:42:30 EDT 2002
Fri Jun 07 08:42:30 EDT 2002
DAY_OF_YEAR: 151
Mon May 27 08:42:30 EDT 2002
Fri May 31 08:42:30 EDT 2002
DAY_OF_YEAR: 144
Mon May 20 08:42:30 EDT 2002
Fri May 24 08:42:30 EDT 2002
DAY_OF_YEAR: 137
Mon May 13 08:42:30 EDT 2002
Fri May 17 08:42:30 EDT 2002
Mon May 13 08:42:30 EDT 2002
Fri May 17 08:42:30 EDT 2002
DAY_OF_YEAR: 130
Mon May 06 08:42:30 EDT 2002
Fri May 10 08:42:30 EDT 2002
DAY_OF_YEAR: 123

Any thoughts?