Java study notes 22 (Date and DateFormat), learning notes dateformat

Java study notes 22 (Date and DateFormat), learning notes dateformat

Date, time, and Date.UtilPackage, not in the SQL package

Date: indicates the specified time, accurate to milliseconds (1000 milliseconds = 1 second)

The time and date operations are based on the millisecond value.

Time origin:January 1, 1970 00:00:00, corresponding to the millisecond value 0

Get the millisecond value of the current time:

Public class DateDemo {public static void main (String [] args) {long l = System. currentTimeMillis (); // obtain the millisecond value of the current date System. out. println (l); // 1515639742854 }}

 

Construction Method of the Date class:

Package demo; import java. util. date; public class DateDemo {public static void main (String [] args) {function1 (); function2 ();} public static void function1 () {Date date = new Date (); System. out. println (date); // output: Thu Jan 11 11:09:41 CST 2018} public static void function2 () {Date date = new Date (123456); System. out. println (date); // output: Thu Jan 01 08:02:03 CST 1970 }}

 

Date method:

Package demo; import java. util. date; public class DateDemo {public static void main (String [] args) {function1 (); function2 ();} public static void function1 () {// convert Date to millisecond date Date = new date (); long time = Date. getTime (); System. out. println (time); // 1515642454307} public static void function2 () {// convert the millisecond to Date date Date = new Date (); System. out. println (date); // Thu Jan 11 11:47:34 CST 2018 date. setTime (123123); System. out. println (date); // Thu Jan 01 08:02:03 CST 1970 }}

 

 

We found that the Date format obtained by the Date class is not what we are used,

Therefore, the DateFormat class provides the date Formatting Function:

DateFormat is an abstract class. It mainly uses its subclass SimpleDateFormat class.

Example:

Package demo; import java. text. dateFormat; import java. text. simpleDateFormat; import java. util. date; // format the public class SimpleDateFormatDemo {public static void main (String [] args) {function ();} public static void function () {DateFormat date = new SimpleDateFormat ("MM dd, yyyy, HH: mm min ss seconds"); String date1 = date. format (new Date (); System. out. println (date1); // output:, January 1, January 11, 2018, 30 seconds }}

 

You can also convert a string to a date:

Example:

Package demo; import java. text. dateFormat; import java. text. parseException; import java. text. simpleDateFormat; import java. util. date; // format the public class SimpleDateFormatDemo {public static void main (String [] args) throws ParseException {function ();} public static void function () throws ParseException {// here is an exception. The following section describes DateFormat date1 = new SimpleDateFormat ("yyyy-MM-dd "); // The string must be in the standard format Date date2 = date1.parse (""); System. out. println (date2); // output: Sat Nov 25 00:00:00 CST 2017 }}

In actual development, users are not allowed to enter their own date, because there is a risk of incorrect format.

Generally, a date control is used for user selection, instead of for user input.