Java date conversion details and example code
- 2020-05-16 06:57:48
- OfStack
Java date conversion
Core classes involved: Date class, SimpleDateFormat class, Calendar class
1.Date and long
Conversion from the Date type to the long type
Date date = new Date(); // gets the current time of type Date
long date2long = date. getTime (); / / Date long
Conversion from the long type to the Date type
long cur = System. currentTimeMills (); // returns the current time of type long
Date long2date = new Date(cur); / / long Date
2. Date and String
Conversion from type Date to type String
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 turn String
Conversion from type String to type Date
String str = "2001-11-03 11:12:33. 828"; // sets the initial string type date
Date str2date = sdf. parse (str); / / String Date
3. Date and Calendar
Conversion from type Date to type Calendar
Calendar cal = Calendar. getInstance (); // gets the current time of type Calendar
cal. setTime (date); / / Date Calendar
Conversion from Calendar type to Date type
Calendar cal = Calendar. getInstance (); // gets the current time of type Calendar
Date cal2date = cal. getTime (); / / Calendar Date
4. To summarize
The conversion between String and the base type depends on the String.valueOf () method The conversion between the Date and String classes depends on the SimpleDateFormat class The Date to long conversion relies on the constructs provided by Date and the getTime() method The conversion from Date to Calendar relies on the setTime() and getTime() methods provided by Calendar5. The interview questions
Q: write 1 method with the parameter Date date, push date back 3 days, and return the string type in the "yyyy-mm-dd" format
public String add3Day(Date date) throws ParseException{
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar cal = Calendar.getInstance();
cal.setTime(date);//Date convert Calendar
cal.add(Calendar.DATE, 3);// Push back the date 3 Day, reduce the 3 Day, -3. To increase the Calendar.MONTH
String after = sdf.format(cal.getTime());//Calendar convert Date And then convert to String
return after;
}
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