API Type Date time before 1.jdk 8
①System class with currentTimeMillis ();
②java.util.Date and subclasses a java.sql.Date
③SimpleDateFormat
④Calendar
2.SimpleDateFormat use
SimpleDateFormat use, SimpleDateFormat to date Date format and parsing of class
1. format, date ---> string
2. parsing, formatting the inverse process, string ---> Date
@Test
public void testSimpleDateFormat () throws a ParseException {
// instantiate the SimpleDateFormat
the SimpleDateFormat the SimpleDateFormat SDF new new = ();
// --- formatted date> string
a Date = new new DATE a Date ();
System.out.println (DATE) ; // Thu Jul 18 21:41:57 CST 2019
String format = sdf.format (DATE);
System.out.println (format); // 19-7-18 9:41 pm
// parse
String str = " 19-10-18 4:17 pm ";
a Date date1 = sdf.parse (str);
System.out.println (date1); // Fri Oct 18 16:17:00 CST 2019
// ****** ******* formatting and parsing manner specified: it invokes the parameterized constructor ********
// the SimpleDateFormat the SimpleDateFormat new new SDF-I = ( "GGG yyyyy.MMMMM.dd HH: mm AAA" );
the SimpleDateFormat the SimpleDateFormat new new SDF-I = ( "the mM-dd-YYYY HH: mm: SS");
Sdf1.format format1 = String (DATE);
System.out.println (format1); 2019-07-18 09:41:57 //
// parse: string must conform to the format requirement SimpleDateFormat identified (by construction parameters reflect), otherwise it will throw an exception
a Date that represented by DATE2 = sdf1.parse ( "2019-07-18 04:30:05");
System.out.println (that represented by DATE2); // Thu Jul 18 04:30:05 CST 2019
}
3. Exercise 1: string "2019-07-18" into java.sql.Date
@Test
public void test1() throws ParseException {
String birth="2019-07-18";
SimpleDateFormat sdf1=new SimpleDateFormat("yyyy-MM-dd");
Date date=sdf1.parse(birth);
System.out.println(date); //Thu Jul 18 00:00:00 CST 2019
java.sql.Date birthDate = new java.sql.Date(date.getTime());
System.out.println(birthDate); //2019-07-18
}
4. Exercise Two: fisherman, "three days of fishing two days of drying" 1990-01-01 From the beginning, in a certain period after he was still fishing nets drying? For example 2020-09-08
Ideas: conversion of a few milliseconds ( one day = 24 hour = 24 * 60 minute = Measured 24 * 60 * 60 second = 24 * 60 * 60 * 1000 ms )
Specific code implementation:
@Test
public void test2() throws ParseException {
SimpleDateFormat sdf1 =new SimpleDateFormat("yyyy-MM-dd");
Date date1 =sdf1.parse("1990-01-01");
//System.out.println(date1.getTime()); //631123200000
SimpleDateFormat sdf2 =new SimpleDateFormat("yyyy-MM-dd");
Date date2 =sdf1.parse("2020-09-08");
//System.out.println(date2.getTime()); //1599494400000
//计算总天数
long date= (date2.getTime() - date1.getTime())/(1000 * 60 * 60 *24);
//System.out.println(date); //11208
long l=date%5;
//System.out.println(l); //3
if(l==1 || l==2 ||l==3){
System.out.println("渔夫打渔");
}else {
System.out.println ( "Fisherman drying net");
}
}
Use 5.Calendar class calendar
Note that when you get in January, January is 0, February is 1, and so, on December 11, when acquiring the week, Sunday is 1, Monday is 2, and so on, Saturday is 7
@Test
public void testCalendar () {
//. 1. Instantiation, which is abstract and can not be directly instantiated
// a manner to create subclasses (the GregorianCalendar) object
// second approach, which call the static method getInstance ()
= Calendar.getInstance Calendar Calendar ();
System.out.println (calendar.getClass ()); subclasses of the object is equivalent // class java.util.GregorianCalendar created
. @ 2 conventional method
// GET ()
int day = calendar.get (Calendar.DAY_OF_MONTH); // get today is the first few days of the month
System.out.println (Day); // 18
System.out.println (Calendar.get (the Calendar.DAY_OF_WEEK)) ;. 5 //
// SET ()
calendar.set (Calendar.DAY_OF_MONTH, 23 is);
Day = Calendar.get (Calendar.DAY_OF_MONTH);
System.out.println (Day); // 23 is
// the Add ()
calendar.add(Calendar.DAY_OF_MONTH,3);//修改的是calendar本身
day=calendar.get(Calendar.DAY_OF_MONTH);
System.out.println(day); //26
calendar.add(Calendar.DAY_OF_MONTH,-3);
day=calendar.get(Calendar.DAY_OF_MONTH);
System.out.println(day); //23
//getTime() 日历类 ---> Date
Date date=calendar.getTime();
System.out.println(date); //Tue Jul 23 21:50:21 CST 2019
//setTime() Date --->日历类
Date date1=new Date();
calendar.setTime(date1);
day=calendar.get(Calendar.DAY_OF_MONTH);
System.out.println(day); //18
}
6.jdk 8 new date and time API
To increase the reason for the new date and time API:
① variability, date, time of such classes should be immutable
② there is an offset of, Date of the year from the beginning of 1900, a month starting from 0
③ formatting, formatting is only useful for Date, Calendar then No
④ not thread-safe, and so can not handle leap seconds
offset can cause incorrect code to achieve more specific see below:
@Test
public void testDate(){
Date date1=new Date(2020,9,8);
System.out.println(date1); //Fri Oct 08 00:00:00 CST 3920
Date date2=new Date(2020-1900,9,8);
System.out.println(date2); //Thu Oct 08 00:00:00 CST 2020
}
jdk 8 new API --LocalDate, LocalTime, LocalDateTime etc.
LocalDate, LocalTime, LocalDateTime using the following categories:
@Test
public void test1 () {
// now (): Get the current date, time, date + time
the LocalDate localDate LocalDate.now = ();
System.out.println (localDate); // 2019-07-18
LocalTime = LocalTime.now localTime, ();
System.out.println (localTime,); //20:34:18.986
the LocalDateTime LocalDateTime.now LocalDateTime = ();
System.out.println (LocalDateTime); // 2019-07-18T20: 34 is: 18.986
// of (): set the specified year, month, day, hour, minutes, seconds, do not offset
the LocalDateTime localDateTime1 = LocalDateTime.of (2020,10,19,20,33,40);
the System. Out.println (localDateTime1); // 2020-10-19T20: 33 is: 40
// getXXX () Gets related properties
System.out.println (localDateTime.getDayOfMonth ()); // 18 this is the first of several month day
System.out.println (localDateTime.getDayOfWeek ()); // THURSDAY currently several weeks week
System.out.println (localDateTime.getMonth ()); // JULY currently few months
System.out.println (localDateTime.getMonthValue ()); // 7 digital form the current month
System.out.println (localDateTime.getHour ()); // current 20 hours
System.out.println (localDateTime.getMinute ()); // 39 current minute
System.out.println (localDateTime.getSecond ()); // 35 seconds current
/ / reflected immutability, modify return value itself does not modify
// withxxx (): set attributes associated
the localDate localDate1 = localDate.withDayOfMonth (26 is);
System.out.println (localDate); // 2019-07-18
System.out.println (localDate1); // 2019-07-26
Localdateti to localdatetime2 = is localdatetime.withho (4);
System.out.println (localdateti OMe); //2019-07-18T20:49:31.531
System.out.println (localdatetime2); //2019-07-18T04:49:31.531
//设置加
localdateti to localdatetime3 = localdatetime.plusmonths (3);
System.out.println (localdateti OMe); //2019-07-18T20:53:55.526
System.out.println (localdatetime3); //2019-10-18T20:53:55.526
//设置减
localdateti to localdatetime4 = localdatetime.minusdays (5);
System.out.println (localdateti OMe); //2019-07-18T20:56:12.180
System.out.println (localdatetime4); //2019-07-13T20:56:12.180
}
Date and time to be extra careful when using.