How to gain Calendar type to String type in java

public static String getYYMM() {
Calendar cal = new GregorianCalendar();
StringBuffer sb = new StringBuffer();
sb.append(cal.get(Calendar.YEAR));

int month = cal.get(Calendar.MONTH) + 1;
String mon = month < 10 ? "0" + month : "" + month;
sb.append(mon);

return sb.toString();
}

public static String getYYYYMMDD() {
Calendar cal = new GregorianCalendar();
SimpleDateFormat format = new SimpleDateFormat("yyyyMMdd");
return format.format(cal.getTime());
}