public static void main(String[] args) {
    Calendar preDate = Calendar.getInstance();
    Calendar now = Calendar.getInstance();
    preDate.set(2007, 0, 1);// 月份从0开始
        
    String year = (now.get(Calendar.YEAR) - preDate.get(Calendar.YEAR)) + "";
    String month = (now.get(Calendar.MONTH) - preDate.get(Calendar.MONTH)) + "";
        
    year = year.length() == 1 ? "0" + year : year;
    month = month.length() == 1 ? "0" + month : month;
        
    System.out.println(year + month);
}

------解决方案--------------------
SimpleDateFormat 名字 = new SimpleDateFormat("yyyyMMdd");

System.out.println(名字.format(new Date()));
生成的就是20080821