java date相关

public static void getPreDay() throws ParseException{   
    String dateStr="2013-1-1";    
    Date date=formatToDate(dateStr, "yyyy-MM-dd");    
    System.out.println(dateStr);    
    
    Calendar calendar = Calendar.getInstance();    
    calendar.setTime(date);    
    calendar.add(Calendar.DATE, -1);    //得到前一天    
    //calendar.add(Calendar.MONTH, -1);    //得到前一个月    System.out.println(formatToString(calendar.getTime(), "yyyy-MM-dd"));   
}    public static Date formatToDate(String strDate,String format) throws ParseException{   
    DateFormat df=new SimpleDateFormat(format);    
    return df.parse(strDate);    
}public static String formatToString(Date date,String format){   
    DateFormat df=new SimpleDateFormat(format);    
    return df.format(date);    
}