JAVA日期處裡

簡單來說，如果要設定日期的話利用Calendar來處理
取今天日期用Date就可
至於日期格式就要利用SimpleDateFormat來處理了

package edu.test;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class Test{
    
    public static void main(String args[]){
     //假設要處理民國101年2月的字串"10102", 取得西元年份與月份
     int year = Integer.parseInt("10102".substring(0, 3))+1911;
     int month = Integer.parseInt("10102".substring(3, 5))-1;
     
     Calendar cal = Calendar.getInstance();
     
     //end:截止日期為"10102"的最後一日
     Date end = null;
     cal.set(year,month, 01);
     cal.set(Calendar.DAY_OF_MONTH,cal.getActualMaximum(Calendar.DAY_OF_MONTH));
     end = cal.getTime();
     System.out.println("偷印看看cal長怎樣 => "+cal);
     
     //beg:起始日期為"10102"減五個月的最後一日
     Date beg = null;
     cal.add(Calendar.MONTH,-5);
     cal.set(Calendar.DAY_OF_MONTH,cal.getActualMaximum(Calendar.DAY_OF_MONTH));
     beg = cal.getTime();
     System.out.println("偷印看看cal長怎樣 => "+cal);
     
     System.out.println("西元年(Date) => "+beg+", "+end);
     
     //Date轉String, 並利用SimpleDateFormat
     SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd");
     System.out.println("西元年(String) => "+sdf.format(beg)+", "+sdf.format(end));
     
     //now:現在日期
     Date now = new Date();
     System.out.println("現在日期西元年(String) => "+sdf.format(now));
    }

}

OUTPUT:

偷印看看cal長怎樣 => java.util.GregorianCalendar[time=1330522727243,areFieldsSet=true,areAllFieldsSet=false,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Taipei",offset=28800000,dstSavings=0,useDaylight=false,transitions=42,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2012,MONTH=1,WEEK_OF_YEAR=9,WEEK_OF_MONTH=5,DAY_OF_MONTH=29,DAY_OF_YEAR=60,DAY_OF_WEEK=4,DAY_OF_WEEK_IN_MONTH=5,AM_PM=1,HOUR=9,HOUR_OF_DAY=21,MINUTE=38,SECOND=47,MILLISECOND=243,ZONE_OFFSET=28800000,DST_OFFSET=0]
偷印看看cal長怎樣 => java.util.GregorianCalendar[time=1317389927243,areFieldsSet=true,areAllFieldsSet=false,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Taipei",offset=28800000,dstSavings=0,useDaylight=false,transitions=42,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2011,MONTH=8,WEEK_OF_YEAR=40,WEEK_OF_MONTH=5,DAY_OF_MONTH=30,DAY_OF_YEAR=273,DAY_OF_WEEK=6,DAY_OF_WEEK_IN_MONTH=5,AM_PM=1,HOUR=9,HOUR_OF_DAY=21,MINUTE=38,SECOND=47,MILLISECOND=243,ZONE_OFFSET=28800000,DST_OFFSET=0]
西元年(Date) => Fri Sep 30 21:38:47 CST 2011, Wed Feb 29 21:38:47 CST 2012
西元年(String) => 2011/09/30, 2012/02/29
現在日期西元年(String) => 2013/01/09