一些无聊的代码之一：JAVA中的日期计算
类别: JAVA教程 
/* * DateCalculate.java , Created on 2005-3-18 * Copyright 2005 AAA Information Technology CO.LTD. All rights reserved. * * 作成日期: 2005-3-18 * 修改履历: * */package com.bjb.xyh.util;
import java.text.DecimalFormat;//import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.Date;
/** * 类描述：自己实现的日期计算类，可以自由扩展 * @author xieyh lamp5w@yahoo.com.cn * @version build 2005-3-18 * */public class DateCalculate { /** 注意格里历和儒略历交接时的日期差别 */ private static transient int gregorianCutoverYear = 1582; /** 闰年中每月天数 */ private static final int[] DAYS_P_MONTH_LY= {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; /** 平年中每月天数 */ private static final int[] DAYS_P_MONTH_CY= {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; /** 代表数组里的年、月、日 */ private static final int Y = 0, M = 1, D = 2; /** 参与运算用 */ private int[] ymd = null;
/** * 检查传入的参数是否合法的日期 * @param date * @throws IllegalArgumentException */ public static void validate(String date)throws IllegalArgumentException{ int[] ymd = splitYMD( date ); if( ymd[M] == 0 || ymd[M] > 12 ){ throw new IllegalArgumentException("月份数值错误"); } if( true == isLeapYear( ymd[0] ) ){ if( ymd[D] == 0 || ymd[D] > DAYS_P_MONTH_LY[ymd[M] -1 ] ){ throw new IllegalArgumentException("日期数值错误"); } }else{ if( ymd[D] == 0 || ymd[D] > DAYS_P_MONTH_CY[ymd[M] -1 ] ){ throw new IllegalArgumentException("日期数值错误"); } } }
/** * 检查传入的参数代表的年份是否为闰年 * @param year * @return */ public static boolean isLeapYear(int year) { return year >= gregorianCutoverYear ? ((year%4 == 0) && ((year%100 != 0) || (year%400 == 0))) : // Gregorian (year%4 == 0); // Julian } /** * 日期加1天，注意这里没有考虑儒略历和格里历交接时相差的10天 * @param year * @param month * @param day * @return */ private int[] addOneDay(int year, int month, int day){ if(isLeapYear( year )){ day++; if( day > DAYS_P_MONTH_LY[month -1 ] ){ month++; if(month > 12){ year++; month = 1; } day = 1; } }else{ day++; if( day > DAYS_P_MONTH_CY[month -1 ] ){ month++; if(month > 12){ year++; month = 1; } day = 1; } } int[] ymd = {year, month, day}; return ymd; } /** * 以循环的方式计算日期加法 * @param date * @param days * @return */ public String addDaysByLoop(String date, int days){ validate(date); int[] ymd = splitYMD( date ); for(int i = 0; i < days; i++){ ymd = addOneDay(ymd[Y], ymd[M], ymd[D]); } return formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay(ymd[D]); } /** * 日期减1天，注意这里没有考虑儒略历和格里历交接时相差的10天 * @param year * @param month * @param day * @return */ private int[] reduceOneDay(int year, int month, int day){ if(isLeapYear( year )){ day--; if( day <= 0 ){ month--; if(month < 1){ year--; month = 12; } day = DAYS_P_MONTH_LY[month -1 ]; } }else{ day--; if( day <= 0 ){ month--; if(month < 1){ year--; month = 12; } day = DAYS_P_MONTH_CY[month -1 ]; } } int[] ymd = {year, month, day}; return ymd; } /** * 以循环的方式计算日期减法 * @param date * @param days * @return */ public String reduceDaysByLoop(String date, int days){ validate(date); int[] ymd = splitYMD( date ); for(int i = 0; i < days; i++){ ymd = reduceOneDay(ymd[Y], ymd[M], ymd[D]); } return formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay(ymd[D]); } /** * 指定日期加上指定的天数的操作 * @param date * @param days * @return * @throws IllegalArgumentException */ public String addDays(Date date, int days) throws IllegalArgumentException{ return addDays(formatDate(date), days); } /** * 指定日期加上指定的天数的操作 * @param date * @param days * @return * @throws IllegalArgumentException */ public String addDays(String date, int days) throws IllegalArgumentException{ validate(date); ymd = splitYMD( date ); if( isLeapYear( ymd[Y] ) ){ ymd[D] += days; if( ymd[D] > DAYS_P_MONTH_LY[ymd[M] -1 ] ){ ymd[M] ++; ymd[D] = ymd[D] - DAYS_P_MONTH_LY[ymd[M] -1-1 ]; if(ymd[M] > 12){ ymd[M] -= 12; ymd[Y]++; } if( ymd[D] > DAYS_P_MONTH_LY[ymd[M] -1 ] ){ addDays(formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay(DAYS_P_MONTH_LY[ymd[M] -1 ]), ymd[D] - DAYS_P_MONTH_LY[ymd[M] -1 ]); } } }else{ ymd[D] += days; if( ymd[D] > DAYS_P_MONTH_CY[ymd[M] -1 ] ){ ymd[M] ++; ymd[D] = ymd[D] - DAYS_P_MONTH_CY[ymd[M] -1-1 ]; if(ymd[M] > 12){ ymd[M] -= 12; ymd[Y]++; } if( ymd[D] > DAYS_P_MONTH_CY[ymd[M] -1 ] ){ addDays(formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay(DAYS_P_MONTH_CY[ymd[M] -1 ]), ymd[D] - DAYS_P_MONTH_CY[ymd[M] -1 ]); } } } return formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay(ymd[D]); } /** * 指定日期减去指定的天数的操作 * @param date * @param days * @return * @throws IllegalArgumentException */ public String reduceDays(Date date, int days) throws IllegalArgumentException{ return reduceDays(formatDate(date), days); } /** * 指定日期减去指定的天数的操作 * @param date * @param days * @return * @throws IllegalArgumentException */ public String reduceDays(String date, int days) throws IllegalArgumentException{ validate(date); ymd = splitYMD( date ); if( isLeapYear( ymd[Y] ) ){ ymd[D] -= days; if( ymd[D] <= 0 ){ ymd[M] --; if(ymd[M] < 1){ ymd[M] += 12; ymd[Y]--; } ymd[D] = ymd[D] + DAYS_P_MONTH_LY[ ymd[M]-1 ]; if( ymd[D] <= 0 ){ reduceDays(formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay( 1 ), abs( ymd[D] - 1 )); } } }else{ ymd[D] -= days; if( ymd[D] <= 0 ){ ymd[M] --; if(ymd[M] < 1){ ymd[M] += 12; ymd[Y]--; } ymd[D] = ymd[D] + DAYS_P_MONTH_CY[ ymd[M]-1 ]; if( ymd[D] <= 0 ){ reduceDays(formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay(1), abs( ymd[D] - 1 )); } } } return formatYear(ymd[Y])+ formatMonthDay(ymd[M])+ formatMonthDay(ymd[D]); } /** * 格式化一个日期字符串 * @param date * @return */ public static String formatDate(Date date){ SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd"); return sdf.format( date ); } /** * 将代表日期的字符串分割为代表年月日的整形数组 * @param date * @return */ public static int[] splitYMD(String date){ int[] ymd = {0, 0, 0}; ymd[Y] = Integer.parseInt(date.substring(0, 4)); ymd[M] = Integer.parseInt(date.substring(4, 6)); ymd[D] = Integer.parseInt(date.substring(6, 8)); return ymd; } /** * 将不足两位的月份或日期补足为两位 * @param decimal * @return */ public static String formatMonthDay(int decimal){ DecimalFormat df = new DecimalFormat("00"); return df.format( decimal ); } /** * 将不足四位的年份补足为四位 * @param decimal * @return */ public static String formatYear(int decimal){ DecimalFormat df = new DecimalFormat("0000"); return df.format( decimal ); } /** * 取绝对值操作 * @param num * @return */ public static int abs(int num){ return (num > 0) ? num : -num; } /** * 测试用main函数 * @param args */ public static void main( String[] args ) throws Exception{ String currDate = "20001231"; String currDate2 = "20001231"; int days = -36600; Date date = null; DateCalculate dc = new DateCalculate(); SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd"); date = sdf.parse( currDate2 ); System.out.println(currDate + " + " + abs(days) + "days = " + dc.addDays(currDate, abs(days))); System.out.println(currDate + " - " + abs(days) + "days = " + dc.reduceDays(currDate, abs(days)));
Calendar cld = Calendar.getInstance(); cld.setTime( date ); cld.add(Calendar.DATE, abs(days)); System.out.println(currDate2 + " + " + abs(days) + "days = " + sdf.format(cld.getTime())); cld = Calendar.getInstance(); cld.setTime( date ); cld.add(Calendar.DATE, days); System.out.println(currDate2 + " - " + abs(days) + "days = " + sdf.format(cld.getTime())); System.out.println(dc.addDaysByLoop(currDate2, abs(days))); System.out.println(dc.reduceDaysByLoop(currDate2, abs(days))); }}
写这些代码的动机来自最近学习SHELL脚本的感受。
目的如下，先搁着，等有时间再作补充：1. 避免递归算法的滥用2. 临界值的把握3. 日期计算的细节
