@Test
  public void test4(){
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
 
    /*
     * 獲取15天后是多少號?
     *
     * add(int field,int n)
     * 為當前calendar指定時間分量上累加給定值
     * 若傳入的是負數(shù)，則是累減
     */
    Calendar calendar = Calendar.getInstance();
    calendar.add(Calendar.DAY_OF_YEAR, 15); //給當前時間加15天
    //System.out.println(calendar.getTime());
    System.out.println(sdf.format(calendar.getTime()));
 
 
    /*
     * 三個月零十天后的那周的星期三是幾號?
     */
    Calendar cal = Calendar.getInstance();
    cal.add(Calendar.MONTH, 3); //給當前時間加3個月
    cal.add(Calendar.DAY_OF_YEAR, 10); //給當前時間加10天
    //得出三個月十天后的日期，然后將日期設為當周星期三
    cal.set(Calendar.DAY_OF_WEEK, 4); //1是周天，所以4是周三
    //System.out.println(cal.getTime());
    System.out.println(sdf.format(cal.getTime()));
 
 
    /*
     * 獲取某個時間分量所允許的最大值
     * 獲取今年最大天數(shù)
     */
    Calendar cal1 = Calendar.getInstance();
    int days = cal1.getActualMaximum(Calendar.DAY_OF_YEAR);
    System.out.println("今年最大天數(shù)為："+days+"天");
 
    /*
     * 一周的第一天是星期日
     * 獲取當前是星期幾
     */
    Calendar cal2 = Calendar.getInstance();
    int w = cal2.get(Calendar.DAY_OF_WEEK);
    System.out.println("今天是星期："+(w==1?7:w-1));
  }

/**** 
* 傳入具體日期 ，返回具體日期增加一個月。 
* @param date 日期(2017-04-13) 
* @return 2017-05-13
* @throws ParseException 
*/ 
private String subMonth(String date) throws ParseException { 
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); 
Date dt = sdf.parse(date); 
Calendar rightNow = Calendar.getInstance(); 
rightNow.setTime(dt); 
rightNow.add(Calendar.MONTH, 1); 
Date dt1 = rightNow.getTime(); 
String reStr = sdf.format(dt1); 
return reStr;

// 使用默認時區(qū)和語言環(huán)境獲得一個日歷
Calendar cal = Calendar.getInstance();
// 賦值時年月日時分秒常用的6個值，注意月份下標從0開始，所以取月份要+1
System.out.println("年:" + cal.get(Calendar.YEAR));
System.out.println("月:" + (cal.get(Calendar.MONTH) + 1)); 
System.out.println("日:" + cal.get(Calendar.DAY_OF_MONTH));
System.out.println("時:" + cal.get(Calendar.HOUR_OF_DAY));
System.out.println("分:" + cal.get(Calendar.MINUTE));
System.out.println("秒:" + cal.get(Calendar.SECOND));

Calendar cal = Calendar.getInstance();
// 如果想設置為某個日期，可以一次設置年月日時分秒，由于月份下標從0開始賦值月份要-1
// cal.set(year, month, date, hourOfDay, minute, second);
cal.set(2018, 1, 15, 23, 59, 59);

// 或者6個字段分別進行設置，由于月份下標從0開始賦值月份要-1
cal.set(Calendar.YEAR, 2018);
cal.set(Calendar.MONTH, Calendar.FEBRUARY);
cal.set(Calendar.DAY_OF_MONTH, 15);
cal.set(Calendar.HOUR_OF_DAY, 23);
cal.set(Calendar.MINUTE, 59);
cal.set(Calendar.SECOND, 59);
System.out.println(cal.getTime());

Calendar cal = Calendar.getInstance();
System.out.println(cal.getTime());
cal.set(2018, 1, 15, 23, 59, 59);
cal.add(Calendar.SECOND, 1);
System.out.println(cal.getTime());

Calendar cal = Calendar.getInstance();
cal.set(2018, 1, 31, 8, 0, 0);
System.out.println(cal.getTime());
cal.add(Calendar.MONTH, 1);
System.out.println(cal.getTime());