Common Java Date Methods collection (Part One)

1. Calculate the maximum number of days in a January:

Calendar time=calendar.getinstance ();　　
time.clear ();
Time.set (calendar.year,year);//year is int
time.set (calendar.month,i-1);/Note that Calendar object defaults to January of 0 
  
   int Day=time.getactualmaximum (calendar.day_of_month);//Days of the Month
  

Note: Before using the Set method, you must clear it, otherwise many of the information will be inherited from the system current time

Conversion of 2.Calendar and date:

(1) Calendar conversion to date:

Calendar cal=calendar.getinstance ();
Date date=cal.gettime ();

(2) Date converted to calendar:

Date Date=new date ();　　
Calendar cal=calendar.getinstance ();
cal.settime (date);

3. Format the output date time (more of this):

Date Date=new date ();　　
SimpleDateFormat df=new SimpleDateFormat ("Yyyy-mm-dd hh:mm:ss");　　
String Time=df.format (date);
System.out.println (time);

4. Calculation of the first week of the year:

(1) to calculate the day of the year is the first week:

Calendar cal=calendar.getinstance ();　　
Cal.set (Calendar.year, 2006);　　
Cal.set (Calendar.month, 8);　　
Cal.set (Calendar.day_of_month, 3);
int Weekno=cal.get (calendar.week_of_year);