Java Date conversion Detailed and instance code _java

Java Date Conversion

Core classes involved: Date class, SimpleDateFormat class, Calendar class

Date type and long type

The date type is converted to a long type

Date date = new Date ();//Get Current time Date type

Long Date2long = Date.gettime ();//date long

Long converts to date type

Long cur = system.currenttimemills ();//Get current time long return

Date long2date = new date (cur);//long to date

Date type and String type

The date type is converted to a string type

Date date = new Date ();

SimpleDateFormat SDF = new SimpleDateFormat ("Yyyy-mm-dd HH:mm:ss". SSS ");//Set the target conversion format to YYYY-MM-DD HH:mm:ss. SSS

String date2string = Sdf.format (date);//date to String

string conversion to date type

String str= "2001-11-03 11:12:33.828";//Set initial string type Date

Date Str2date=sdf.parse (str);//string to date

Date Type and calendar type

The date type is converted to a calendar type

Calendar cal = Calendar.getinstance ();//Get current time calendar type

Cal.settime (date); Date Change Calendar

The calendar type converts to the date type

Calendar cal = Calendar.getinstance ();//Get current time calendar type

Date cal2date = Cal.gettime ();//calendar to date

Iv. Summary

1. The conversion between string and base type depends on the string.valueof () method
2. The conversion between date and string classes depends on the SimpleDateFormat class
3. Date and long conversions rely on date-provided constructs and the gettime () method
4. Date and calendar conversions depend on the settime () and gettime () methods provided by the calendar.
   

Five, interview questions

Q: Write a method, the parameter is date date, push date back 3 days, return the string type in "YYYY-MM-DD" format

Public String add3day (date date) throws parseexception{
  SimpleDateFormat sdf = new SimpleDateFormat ("Yyyy-mm-dd"); C2/>calendar cal = Calendar.getinstance ();
  Cal.settime (date);//date convert to Calendar
  cal.add (calendar.date, 3);//Push the date back 3 days, reduce 3 days-3. Monthly increase is calendar.month
  after = Sdf.format (Cal.gettime ()),//calendar converted to date, and then converted to string return after
  ;
}

Thank you for reading, I hope to help you, thank you for your support for this site!