Java date conversion

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

1. Date type and long type

Date type is converted to long type

Date date = new Date();//Get the current time Date type

long date2long = date.getTime();//Convert Date to long

long type to Date type

long cur = System.currentTimeMills();//Get the current time long type and return

Date long2date = new Date(cur ; 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 type to Date type

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

Date str2date=sdf.parse(str);//Convert String to Date

3. Date type Convert Calendar type

Date type to Calendar type

Calendar cal = Calendar.getInstance(); //Get the current time Calendar type

cal.setTime(date); //Date to Calendar

Calendar type to Date Type

Calendar cal = Calendar.getInstance();//Get the current time Calendar type

Date cal2date = cal.getTime();//Convert Calendar to Date

4. Interview questions

Q: Write a method, parameters It is a Date date, push the date back 3 days, and return the string type in the format of "yyyy-mm-dd"

public String add3Day(Date date) throws ParseException{

Calendar cal = Calendar.getInstance();

cal.add(Calendar.DATE, 3);//Push the date back 3 days, If the days decrease by 3, it will be -3. If the month increases, Calendar.MONTH

return after;

5. Summary

Conversion between String and basic types relies on the String.valueOf() method

Conversion between Date and String classes relies on the SimpleDateFormat class

Conversion between Date and long relies on the construct provided by Date and getTime( ) method

Date and Calendar conversion relies on the setTime() and getTime() methods provided by Calendar