Java Learning Note (Date class, DateFormat Class)

Date, time, and date classes, which are described in the util package instead of in the SQL package

Date: Represents a specific time instantaneous, accurate to milliseconds (1000 milliseconds = 1 seconds)

Time and date operations are based on millisecond values

Time Origin:January 1, 1970, 0:0 0 seconds, corresponding millisecond value is 0

Gets the millisecond value of the current time:

 Public class Datedemo {    publicstaticvoid  main (string[] args) {        long L = system.currenttimemillis ();         // gets the millisecond value of the current date         System.out.println (l);         // 1515639742854     }}

How to construct the date class:

 Packagedemo;Importjava.util.Date; Public classDatedemo { Public Static voidMain (string[] args) {function1 ();    Function2 (); }     Public Static voidfunction1 () {Date Date=NewDate ();        SYSTEM.OUT.PRINTLN (date); //output: Thu Jan 11:09:41 CST 2018    }     Public Static voidfunction2 () {Date Date=NewDate (123456);        SYSTEM.OUT.PRINTLN (date); //output: Thu Jan 08:02:03 CST 1970    }}

Method of the Date class:

 Packagedemo;Importjava.util.Date; Public classDatedemo { Public Static voidMain (string[] args) {function1 ();    Function2 (); }     Public Static voidfunction1 () {//date turns to millisecondsDate Date =NewDate (); LongTime =Date.gettime ();        System.out.println (time); //1515642454307    }     Public Static voidfunction2 () {//Millisecond Turn DateDate Date =NewDate ();        SYSTEM.OUT.PRINTLN (date); //Thu Jan 11:47:34 CST 2018Date.settime (123123);        SYSTEM.OUT.PRINTLN (date); //Thu Jan 08:02:03 CST 1970    }}

We find that the date format is not what we used to be.

So here's a DateFormat class that provides formatting date functionality:

DateFormat is an abstract class that mainly uses its subclass SimpleDateFormat class

Example:

 Packagedemo;ImportJava.text.DateFormat;ImportJava.text.SimpleDateFormat;Importjava.util.Date;//Formatting the date Public classSimpledateformatdemo { Public Static voidMain (string[] args) {function (); }         Public Static voidfunction () {DateFormat date=NewSimpleDateFormat ("yyyy mm month DD Day hh point mm min ss sec"); String Date1= Date.format (NewDate ());        System.out.println (date1); //output: January 11, 2018 12 point 01分钟30秒    }}

You can also convert a string to a date:

Example:

 Packagedemo;ImportJava.text.DateFormat;Importjava.text.ParseException;ImportJava.text.SimpleDateFormat;Importjava.util.Date;//Formatting the date Public classSimpledateformatdemo { Public Static voidMain (string[] args)throwsparseexception {function (); }     Public Static voidfunction ()throwsParseException {//Here are the exceptions, which are described laterDateFormat date1 =NewSimpleDateFormat ("Yyyy-mm-dd"); //must be a standard-format stringDate date2 = Date1.parse ("2017-11-25");        System.out.println (DATE2); //output: Sat 00:00:00 CST    }}

In real-world development, users are not allowed to enter dates themselves because of the risk of formatting errors

You usually make a date control for the user to choose instead of letting the user enter

Java Learning Note (Date class, DateFormat Class)