calendar类，日期加减

转：http://zhujinguo.iteye.com/blog/702013

*  今 天是2006年11月3日 是今年的第307天 c.getTime()的結果: Fri Nov 03 11:31:47 CST 2006 new Date()的結果: Fri Nov 03 11:31:47 CST 2006 17天后是Thu Feb 02 11:31:47 CST 2006

public class test1 {

    public static void main(String[] args) {
          Calendar c = Calendar.getInstance();
          int year=c.get(Calendar.YEAR);


            int month=c.get(Calendar.MONTH)+1;
          int date=c.get(Calendar.DATE);
          System.out.println("今天是"+year+"年"+month+"月"+date+"日");
          System.out.println("是今年的第"+c.get(Calendar.DAY_OF_YEAR)+"天");
          System.out.println("c.getTime()的結果: "+c.getTime());
          System.out.println("new Date()的結果: "+new Date());
          c.set(Calendar.DAY_OF_YEAR, date + 30);
          System.out.println("17天后是"+c.getTime());
      }

}

public class test1 {

    public static void main(String[] args) {
          Calendar c = Calendar.getInstance();
          int year=c.get(Calendar.YEAR);
          

            int month=c.get(Calendar.MONTH)+1;
          int date=c.get(Calendar.DATE);
          System.out.println("今天是"+year+"年"+month+"月"+date+"日");
          System.out.println("是今年的第"+c.get(Calendar.DAY_OF_YEAR)+"天");
          System.out.println("c.getTime()的結果: "+c.getTime());
          System.out.println("new Date()的結果: "+new Date());
          c.set(Calendar.DAY_OF_YEAR, date + 30);
          System.out.println("17天后是"+c.getTime());
      }

}

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

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

注意int month=c.get(Calendar.MONTH)+1哦，好像系统是从0开始计月份，到了12月就归零了。所以单独取月份时，要在后面加一才能得到当前的月份。


calender日期加减后赋值给Date类型

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String time=sdf.format(new Date());
Calendar cd = Calendar.getInstance();

try {
    cd.setTime(sdf.parse(time));
} catch (ParseException e) {
    e.printStackTrace();
}
      cd.add(Calendar.DATE, 1);//增加一天
       //cal.add(Calendar.DATE, -1);      //减一天
       //cd.add(Calendar.MONTH, 1);//增加一月
      Date date=cd.getTime();
      System.out.println(sdf.format(date));

		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
		String time=sdf.format(new Date()); 
		Calendar cd = Calendar.getInstance();
		
		try {
			cd.setTime(sdf.parse(time));
		} catch (ParseException e) {			
			e.printStackTrace();
		}
        cd.add(Calendar.DATE, 1);//增加一天     
         //cal.add(Calendar.DATE, -1);      //减一天 
         //cd.add(Calendar.MONTH, 1);//增加一月 
        Date date=cd.getTime(); 
        System.out.println(sdf.format(date));

将yyyy//MM/dd的字符串类型转为Date类型

str12 = format.parse(str12_1);

							 SimpleDateFormat format = new SimpleDateFormat("yyyy/MM/dd");
							 str12 = format.parse(str12_1);

在excel导入数据时，日期类型的数据直接获取

CellType t1 = st.getCell(11, row).getType();
Date regDate = null;
Date str12=null;//出生年月,不能为空
if (t1 == CellType.DATE)
{
    DateCell regCell = (DateCell) st.getCell(11, row);
    str12 = regCell.getDate();
}