java 字符串String 日期Date 相加、相减

/**日期相加、相减
* @param date 传入字符串日期，例如：2011-01-03
* @param addNumber 传入整数
* @return
* Administrator Mar 10, 2011 2:04:42 PM
*/
public static String getDateAdd(String date, int addNumber) {
String returnStr = "";
StringTokenizer token = new StringTokenizer(date, "-");
int num = token.countTokens();
if (num == 3) {
int year;
int month;
int day;
year = Integer.parseInt(token.nextToken());
month = Integer.parseInt(token.nextToken());
day = Integer.parseInt(token.nextToken());
SimpleDateFormat formatter;
formatter = new SimpleDateFormat("yyyy-MM-dd");
Calendar calen = Calendar.getInstance();
calen.set(year, month - 1, day);
calen.add(5, addNumber); // 5代表日期，1代表年，2代表月
returnStr = formatter.format(calen.getTime());
} else
returnStr = date;
return returnStr;
}