实现代码一：
import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.Date;public class DateTestUtil { public static void main(String[] args) throws Exception { SimpleDateFormat sdf=new SimpleDateFormat("yyyyMMdd"); String str="20110823"; Date dt=sdf.parse(str); Calendar rightNow = Calendar.getInstance(); rightNow.setTime(dt); rightNow.add(Calendar.YEAR,-1);//日期减1年 rightNow.add(Calendar.MONTH,3);//日期加3个月 rightNow.add(Calendar.DAY_OF_YEAR,10);//日期加10天 Date dt1=rightNow.getTime(); String reStr = sdf.format(dt1); System.out.println(reStr); }}注：在Calendar对象的add方法中，第二个参数为正数表示“加”，负数表示“减”。
代码二： java date 日期加减天数
测试类代码：
import java.text.SimpleDateFormat; import java.util.Date; public class DateTest { public static void main(String[] arg){ Date now = new Date(); addAndSubtractDaysByGetTime(now,-5); addAndSubtractDaysByGetTime(now,5); addAndSubtractDaysByCalendar(now,-5); addAndSubtractDaysByCalendar(now,5); } public static Date addAndSubtractDaysByGetTime(Date dateTime/*待处理的日期*/,int n/*加减天数*/){ //日期格式 SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd"); SimpleDateFormat dd=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); System.out.println(df.format(new Date(dateTime.getTime() + n * 24 * 60 * 60 * 1000L))); //System.out.println(dd.format(new Date(dateTime.getTime() + n * 24 * 60 * 60 * 1000L))); //注意这里一定要转换成Long类型，要不n超过25时会出现范围溢出，从而得不到想要的日期值 return new Date(dateTime.getTime() + n * 24 * 60 * 60 * 1000L); } public static Date addAndSubtractDaysByCalendar(Date dateTime/*待处理的日期*/,int n/*加减天数*/){ //日期格式 SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd"); SimpleDateFormat dd=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); java.util.Calendar calstart = java.util.Calendar.getInstance(); calstart.setTime(dateTime); calstart.add(java.util.Calendar.DAY_OF_WEEK, n); System.out.println(df.format(calstart.getTime())); //System.out.println(dd.format(calstart.getTime())); return calstart.getTime(); } }运行结果：
2014-10-06
2014-10-16
2014-10-06
2014-10-16
代码三：
在网上查阅资料，加上自己总结的一些关于Date类的工具类。
package com.data.utils;import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.Date;public class DateFormat { /** * 日期减几年 */ public static String dateMinusYear(String str) throws Exception { SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM"); Date dt = sdf.parse(str); Calendar rightNow = Calendar.getInstance(); rightNow.setTime(dt); rightNow.add(Calendar.YEAR, -1);// 日期减1年 Date dt1 = rightNow.getTime(); String reStr = sdf.format(dt1); return reStr; } /** * 日期加几年 */ public static String dateAddYear(String str) throws Exception { SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM"); Date dt = sdf.parse(str); Calendar rightNow = Calendar.getInstance(); rightNow.setTime(dt); rightNow.add(Calendar.YEAR, 1);// 日期加1年 Date dt1 = rightNow.getTime(); String reStr = sdf.format(dt1); return reStr; } /** * 日期减几月 */ public static String dateMinusMonth(String str) throws Exception { SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM"); Date dt = sdf.parse(str);//将字符串生成Date Calendar rightNow = Calendar.getInstance(); rightNow.setTime(dt);//使用给定的 Date 设置此 Calendar 的时间。 rightNow.add(Calendar.MONTH, -1);// 日期减1个月 Date dt1 = rightNow.getTime();//返回一个表示此 Calendar 时间值的 Date 对象。 String reStr = sdf.format(dt1);//将给定的 Date 格式化为日期/时间字符串，并将结果添加到给定的 StringBuffer。 return reStr; } /** * 日期加几月 */ public static String dateAddMonth(String str) throws Exception { SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM"); Date dt = sdf.parse(str); Calendar rightNow = Calendar.getInstance(); rightNow.setTime(dt); rightNow.add(Calendar.MONTH, 1);// 日期加3个月 // rightNow.add(Calendar.DAY_OF_YEAR,10);//日期加10天 Date dt1 = rightNow.getTime(); String reStr = sdf.format(dt1); return reStr; } /** * 获取当前年月的第一个月的str * @param str * 201505 * @return 201501 * @throws Exception */ public static String dateOneMonth(String str) { str = str.substring(0, str.length() - 2); str = str + "01"; return str; } /** * 算出所选月份距离一月份有几个月。 * @param str 201509 * @return 9 */ public static int dateDistanceMonth(String str) { int i = Integer.parseInt(str); int j = Integer.parseInt(DateFormat.dateOneMonth(str)); System.out.println(i - j); return i - j + 1; } /** * 获取两个时间的时间差，精确到毫秒 * @param str * @return */ public static String TimeDifference(long start, long end) { long between = end - start; long day = between / (24 * 60 * 60 * 1000); long hour = (between / (60 * 60 * 1000) - day * 24); long min = ((between / (60 * 1000)) - day * 24 * 60 - hour * 60); long s = (between / 1000 - day * 24 * 60 * 60 - hour * 60 * 60 - min * 60); long ms = (between - day * 24 * 60 * 60 * 1000 - hour * 60 * 60 * 1000 - min * 60 * 1000 - s * 1000); String timeDifference = day + "天" + hour + "小时" + min + "分" + s + "秒" + ms + "毫秒"; return timeDifference; }} /** * 获取24小时、一周、一个月的起始时间 * * @param timeInterval * : DAY_TIME_INTERVAL WEEK_TIME_INTERVAL MONTH_TIME_INTERVAL * @return "yyyy-mm-dd hh:mm:ss" */ public static String getStartTime(int timeInterval) { Calendar cal = Calendar.getInstance(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); if (DAY_TIME_INTERVAL == timeInterval) {// 获取24小时的起始时间 cal.set(Calendar.HOUR_OF_DAY, 0); cal.set(Calendar.MINUTE, 0); cal.set(Calendar.SECOND, 0); String startTime = sdf.format(cal.getTime()); return startTime; } else if (WEEK_TIME_INTERVAL == timeInterval) { int weekday = cal.get(Calendar.DAY_OF_WEEK) - 1; cal.add(Calendar.DATE, -weekday); cal.set(Calendar.HOUR_OF_DAY, 0); cal.set(Calendar.MINUTE, 0); cal.set(Calendar.SECOND, 0); String startTime = sdf.format(cal.getTime()); return startTime; } else if (MONTH_TIME_INTERVAL == timeInterval) { int dayofmonthMin = cal.getActualMinimum(Calendar.DAY_OF_MONTH); // c.add(Calendar.DATE, -dayofmonth); cal.set(Calendar.DATE, dayofmonthMin); cal.set(Calendar.HOUR_OF_DAY, 0); cal.set(Calendar.MINUTE, 0); cal.set(Calendar.SECOND, 0); String startTime = sdf.format(cal.getTime()); return startTime; } return null; } /** * 获取24小时、一周、一个月的结束时间 * * @param timeInterval * : DAY_TIME_INTERVAL WEEK_TIME_INTERVAL MONTH_TIME_INTERVAL * @return "yyyy-mm-dd hh:mm:ss" */ public static String getEndTime(int timeInterval) { Calendar cal = Calendar.getInstance(); cal.setTimeZone(TimeZone.getTimeZone("GMT+8")); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); if (DAY_TIME_INTERVAL == timeInterval) { cal.set(Calendar.HOUR_OF_DAY, 23); cal.set(12, 59); cal.set(13, 59); long date = cal.getTimeInMillis(); String endTime = sdf.format(new Date(date)); return endTime; } else if (WEEK_TIME_INTERVAL == timeInterval) { int weekday = cal.get(Calendar.DAY_OF_WEEK) - 1; cal.add(Calendar.DATE, -weekday); cal.add(Calendar.DATE, 6); cal.set(Calendar.HOUR_OF_DAY, 23); cal.set(12, 59); cal.set(13, 59); long date = cal.getTimeInMillis(); String endTime = sdf.format(new Date(date)); return endTime; } else if (MONTH_TIME_INTERVAL == timeInterval) { int dayOfMonthMax = cal.getActualMaximum(Calendar.DAY_OF_MONTH); cal.set(Calendar.DATE, dayOfMonthMax); cal.set(Calendar.HOUR_OF_DAY, 23); cal.set(Calendar.MINUTE, 59); cal.set(Calendar.SECOND, 59); String endTime = sdf.format(cal.getTime()); return endTime; } return null; } /** * 判断dateStr是否在start和end中间，start和end都可以为null yyyyMMddHHmmss或者yyyyMMdd格式 * * @author you.xu * @date 2015年8月19日下午3:11:46 * @param dateStr * @param start * @param end * @return */ public static boolean checkDateVal(String dateStr, String start, String end) { boolean isDateRight = false; Date date = null; Date startDate = null; Date endDate = null; SimpleDateFormat sdf = null; // 判断日期格式 if (14 == dateStr.length()) { sdf = new SimpleDateFormat("yyyyMMddHHmmss"); } else if (8 == dateStr.length()) { sdf = new SimpleDateFormat("yyyyMMdd"); } else return false; try { // 更改判断日期格式 date = sdf.parse(dateStr); } catch (ParseException e) { log.error(e, e); } if ((start == null) && (end != null)) { try { endDate = sdf.parse(end); } catch (ParseException ex1) { log.error(ex1, ex1); } if ((date != null) && (endDate != null))// Check parameters for { if (date.compareTo(endDate) <= 0) isDateRight = true; } } else if ((start != null) && (end == null)) { try { startDate = sdf.parse(start); } catch (ParseException ex1) { log.error(ex1, ex1); } if ((date != null) && (startDate != null)) { if (date.compareTo(startDate) >= 0) isDateRight = true; } } else if ((start != null) && (end != null)) { try { startDate = sdf.parse(start); endDate = sdf.parse(end); } catch (ParseException ex2) { System.out.println(ex2.toString()); } if ((startDate != null) && (date != null) && (endDate != null)) { if ((date.compareTo(startDate) >= 0) && (date.compareTo(endDate) <= 0)) isDateRight = true; } } return isDateRight; } /** * 判断dateStr是否在start和end中间，start和end都可以为null long形格式 * * @author you.xu * @date 2015年8月19日下午3:12:35 * @param dateStr * @param start * @param end * @return */ public static boolean checkDateV(String dateStr, String start, String end) { boolean isDateRight = false; long date = -1; long fromDate = -1; long toDate = -1; date = java.lang.Long.parseLong(dateStr); if ((start == null) && (end == null)) { isDateRight = true; } else if ((start == null) && (end != null)) { try { toDate = java.lang.Long.parseLong(end); } catch (NumberFormatException nfe) { log.error(nfe, nfe); } if (date <= toDate) { isDateRight = true; } } else if ((start != null) && (end == null)) { try { fromDate = java.lang.Long.parseLong(start); } catch (NumberFormatException nfe) { log.error(nfe, nfe); } if (date >= fromDate) { isDateRight = true; } } else if ((start != null) && (end != null)) { try { toDate = java.lang.Long.parseLong(end); fromDate = java.lang.Long.parseLong(start); } catch (NumberFormatException nfe) { log.error(nfe, nfe); } if ((date <= toDate) && (date >= fromDate)) { isDateRight = true; } } return isDateRight; }目前就用到了这些，随时添加，有简单方便的时间工具类，希望和大家一起学习，在评论中指出。thanks！！！