Android手机开发：日期函数之判断某日期格式是否之前+计算某日期之前N天或之后N天的日期

/**
* 判断日期格式是否正确
*/
public static boolean IsDateFormat(String dataStr) {
boolean state = false;
try {
java.text.SimpleDateFormat dFormat = new SimpleDateFormat("yyyy-MM-dd");
dFormat.setLenient(false);
java.util.Date d = dFormat.parse(dataStr);
state = true;
} catch (ParseException e) {
e.printStackTrace();
state = false;
}
return state;
}

/**
* 计算date之前n天的日期
*/
public static Date getDateBefore(Date date, int n) {
Calendar now = Calendar.getInstance();
now.setTime(date);
now.set(Calendar.DATE, now.get(Calendar.DATE) - n);
return now.getTime();
}

/**
* 得到几天后的时间
*/
public static Date getDateAfter(Date d, int day) {
Calendar now = Calendar.getInstance();
now.setTime(d);
now.set(Calendar.DATE, now.get(Calendar.DATE) + day);
return now.getTime();
}