Android - 日期类的使用

Android的日期类, Date和Calendar, Date显示, Calendar计算.
处理顺序: String -> Date -> Calendar.
示例实现了几个比较常见的方法:
(1) 日期相隔天数;
(2) 字符串转换Date类;
(3) 获取之前的日期;
(4) 判断是否超过今天等.

代码:

package me.chunyu.Pedometer.manager;    import android.util.Pair;    import java.text.ParseException;  import java.text.SimpleDateFormat;  import java.util.ArrayList;  import java.util.Calendar;  import java.util.Date;  import java.util.Locale;    import me.chunyu.Pedometer.database.counter.DailyData;    /** * 日期管理器, 输入日期的格式"yyyy-MM-dd"的字符串数组, 可能不连续. * 提取步数, 需要把拥有步数的项提取出来, 未有步数的项至为0. * 使用时, 再根据日期进行统计. * <p/> * Created by wangchenlong on 15/8/17. */  public class DateManager {        private static DateManager sInstance; // 单例      private final RecordManager mRecordManager; // 数据管理器      private final SimpleDateFormat sFormatter; // 格式化        private DateManager() {          mRecordManager = RecordManager.getInstance();          sFormatter = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);      }        public static DateManager getInstance() {          if (sInstance == null) {              sInstance = new DateManager();          }          return sInstance;      }        /** * 从RecordManager获取数据, 转换为步数数组, 从当前日期一直至最早日期. * * @return 步数数组[当前日期, 至, 最早日期] */      public ArrayList<Pair<String, Integer>> getDataDates() {          String[] days = mRecordManager.getSortedFilenames();          if (days.length <= 0) {              return null;          }            String firstDay = days[0];          String lastDay = days[days.length - 1];            if (isAfterToday(lastDay)) {              lastDay = sFormatter.format(new Date());          }            long n = daysBetweenTwoDates(firstDay, lastDay) + 1;            ArrayList<Integer> allSteps = new ArrayList<>();          ArrayList<String> allDays = new ArrayList<>();            for (int i = 0; i < n; ++i) {              String perDay = getBeforeDay(lastDay, i);              DailyData dailyData = mRecordManager.getDailySteps(perDay);              if (dailyData != null) {                  int[] steps = dailyData.steps;                  int maxStep = steps[steps.length - 1];                  allSteps.add(maxStep);              } else {                  allSteps.add(0);              }              allDays.add(perDay);          }            ArrayList<Pair<String, Integer>> totalData = new ArrayList<>();          for (int i = 0; i < allSteps.size(); ++i) {              Pair<String, Integer> dateWithStep = Pair.create(allDays.get(i), allSteps.get(i));              totalData.add(dateWithStep);          }            return totalData;      }        /** * 判断两个日期相隔的天数 * * @param earlyDay 较早的日期 * @param lateDay 较晚的日期 * @return 相隔天数 */      public long daysBetweenTwoDates(String earlyDay, String lateDay) {          Date earlyDate = getDateFromStr(earlyDay);          Date lateDate = getDateFromStr(lateDay);            Calendar startCalendar = Calendar.getInstance();          Calendar lateCalendar = Calendar.getInstance();          startCalendar.setTime(earlyDate);          lateCalendar.setTime(lateDate);            long diff = lateCalendar.getTimeInMillis() - startCalendar.getTimeInMillis();            return diff / (24 * 60 * 60 * 1000);      }        /** * 把日期字符串转换为Date类 * * @param day 日期字符串 * @return 日期Data类 */      public Date getDateFromStr(String day) {          Date date;          try {              date = sFormatter.parse(day);          } catch (ParseException e) {              e.printStackTrace();              return null;          }          return date;      }        /** * 获取之前某天的日期 * * @param day 时间基准 * @param i 相差天数 * @return 前几天的日期 */      public String getBeforeDay(String day, int i) {          Date date = getDateFromStr(day);          Calendar calendar = Calendar.getInstance();          calendar.setTime(date);          calendar.add(Calendar.DAY_OF_YEAR, i * (-1));          return sFormatter.format(calendar.getTime());      }        /** * 判断时间是否超过今日 * * @param day 时间 * @return 是否 */      public boolean isAfterToday(String day) {          Date lateDate = getDateFromStr(day);          Date todayDate = new Date();          return lateDate.getTime() > todayDate.getTime();      }  }