日期的加减问题??用Java实现.

Question

int iMonths = 30;Calendar cal=Calendar.getInstance( );
int year = cal.get(Calendar.YEAR); 
int month = cal.get(Calendar.MONTH)+1;
int date = cal.get(Calendar.DATE);
month = month + iMonths;
while (month>12) {
        month = month - 12;
        year = year +1;
}
while (month<1) {
month = month + 12;
year = year - 1;
}strDate = year+"-"+month+"-"+date;dateDate = java.util.Date.valueOf(strDate);

Answer 1

Calendar c = Calendar.getInstance();
c.add(c.MONTH,-30);
System.out.println(""+c.get(c.YEAR)+"-"+(c.get(c.MONTH)+1)+"-"+c.get(c.DATE));

Answer 2

cal.get(Calendar.MONTH)+1;
c.get(c.MONTH)+1
为什么month都要+1啊??