1, JDK8 upgrades the date class and adds the increase or decrease method of the date
private static void JDK8Datetest() {
//Defines the date and time of a string
String s = "2020 00 Nov 11:00:00";
//Static methods return formatted objects
DateTimeFormatter pattern = DateTimeFormatter.ofPattern("yyyy year MM month dd day HH:mm:ss");
//Pass in the string time and format
LocalDateTime parse = LocalDateTime.parse(s, pattern);
//Advance one day based on the current date to get a new date
LocalDateTime localDateTime = parse.plusDays(1);
//Format the new date into a string
String date = localDateTime.format(pattern);
//Output printing
System.out.println(date);//The output result information is: 00:00:00, November 12, 2020
}2, JDK8 get time object
/**
* Before JDK8, we mainly used three classes to process date and time,
* Date
* SimpleDateFormat
* Calendar(Wait for a brief introduction later).
* There are more or less problems in the use of these three classes. For example, SimpleDateFormat is not thread safe,
* For example, the months obtained by Date and Calendar are 0 to 11, rather than 1 to 12 in real life,*/
Date date1 = new Date();
System.out.println(date1.getMonth());// The printing result of month information obtained before jdk1.8: 9 the actual month of the system is 10
//1.jdk8 get the current system time
LocalDateTime now = LocalDateTime.now();
System.out.println(now);//2021-10-11T20:12:55.351
//2.jdk8 get the specified time
LocalDateTime time = LocalDateTime.of(2021, 11, 11, 11, 11, 11);
System.out.println(time);//2021-11-11T11:11:11
/**
* Explanation:
* 1.now():The time obtained is the time of the current system
* 2.of():Method parameters can specify the time
* */3, JDK8 gets each value in time
/**
* JDK8 Gets each value in the time
* LocalDateTime Common methods:
* getYear():Get year minute in time
* getMoth():Gets the month in the time
* getMothValue():Get the month from January to December
* getDayOfYear():Get day 1-31
* getDateOfYear()Get the day of the year
* getDayOfWeek():Gets the English representation of the week. Gets the enumeration value
* getMinute():Hu Oh, go for a minute
* getHour():Get hours
* */
LocalDateTime now1 = LocalDateTime.now();
//Get year
int year = now1.getYear();
System.out.println(year);
//Get the month in English means to get the enumeration value
Month month = now1.getMonth();
System.out.println(month);
//Get month 1-12
int monthValue = now1.getMonthValue();
System.out.println(monthValue);
//Get the day of the month 1-31
int dayOfMonth = now1.getDayOfMonth();
System.out.println(dayOfMonth);
//Get the day of the year 1-366
int dayOfYear = now1.getDayOfYear();
System.out.println(dayOfYear);
// Gets the English representation of the week. Gets the enumeration value
DayOfWeek dayOfWeek = now1.getDayOfWeek();
System.out.println(dayOfWeek);
//Get minutes
int minute = now1.getMinute();
System.out.println(minute);
//Get hours
int hour = now1.getHour();
System.out.println(hour);4, JDK8 time conversion --- only get month, day, hour, minute and second
/**
* JDK8 Time class -- conversion method
* now():Get current system time
* toLocalDate():Show only the date of time
*toLocalTime():Time of war
* */
LocalDateTime now2 = LocalDateTime.now();//Get current system time
//To convert to localDate object, you only need to display the year, month and day information
LocalDate localDate = now2.toLocalDate();
System.out.println(localDate);//2021-10-11
//Convert to localTime object, showing only hours, minutes and seconds
LocalTime localTime = now2.toLocalTime();
System.out.println(localTime);//20:56:14.8355, JDK8 time class formatting and parsing
/**
* JDK8 Time class - formatting and parsing
* */
//Get current system time
LocalDateTime now3 = LocalDateTime.now();
System.out.println(now3);//2021-10-11T21:00:25.758
System.out.println("==============================");
//Formatting requires a formatted Date object datetomefromatter (format)
String format = now.format(DateTimeFormatter.ofPattern("yyyy year MM month dd day HH:mm:ss"));
System.out.println(format);//October 11, 2021 21:02:40
System.out.println("==============================");
//Resolution: String s = "November 11, 2020 0:0:0"// Must be in the same format as specified for resolution
String s1 = "2021 00 Nov 11:00:00";
//Pass in the date string that needs to be parsed
LocalDateTime parse1 = LocalDateTime.parse(s1, DateTimeFormatter.ofPattern("yyyy year MM month dd day HH:mm:ss"));
System.out.println(parse1);//2021-11-11T00:00
System.out.println("==============================");6, JDK8 time class - Method of plus series
//Get current system time
LocalDateTime now = LocalDateTime.now();
//Year + 1
LocalDateTime year = now.plusYears(1); //A positive number or a negative number 0 will do
System.out.println(year.getYear());
//Month + 1
LocalDateTime month = now.plusMonths(1);
System.out.println(month.getMonthValue());
//There are days, hours, minutes, seconds and weeks. The usage of this method is the same7, JDK8 time class - Method of minus series
//Reverse thinking
The parameter is a positive time push forward (It refers to the past time)
The parameter is a negative time push back (It refers to the time in the future)
LocalDateTime now = LocalDateTime.now();
//Passing a positive number is subtracting one year from now, passing - 1 is adding one year to now, and 0 has no meaning
//The new time object LocalDateTime is obtained
LocalDateTime years = now.minusYears(0);
System.out.println(years.getYear());
//Passing a positive number is in the month of now - 1
LocalDateTime month = now.minusMonths(1);
System.out.println(month.getMonthValue());
//The daily hours, minutes, seconds and weeks are consistent8, JDK8 time class - Method of with series
Direct modification time,What you get is a new time object LocalDateTime
LocalDateTime now = LocalDateTime.now();
//Set the number of years to be passed in. If a negative number is passed in, no error will be reported
LocalDateTime year = now.withYear(1);
System.out.println(year);
//Set the value passed in by month, but in January December
LocalDateTime month = now.withMonth(12);
System.out.println(month.getMonthValue());
//Set the day of the month
LocalDateTime day = now.withDayOfMonth(15);
System.out.println(day);
//Displays the day ordinal of the year. The display format is the month ordinal of the year
LocalDateTime dayOfYear = now.withDayOfYear(112);
System.out.println(dayOfYear); 9, JDK8 time class - time interval object
LocalDate date1 = LocalDate.of(2020, 12, 21);
LocalDate date2 = LocalDate.of(2022, 11, 25);
Period between1 = Period.between(date1, date2);
System.out.println(between1);
//P1Y11M4D
//P time interval object 1Y represents a year 11M represents 11 months 4D represents 4 days
// Year when this period is obtained
int years = between1.getYears();
System.out.println(years);
//Get the month when this period
int months = between1.getMonths();
System.out.println(months);
//Gets the number of days during this period
int days = between1.getDays();
System.out.println(days);
//Indicates the total number of months between the two time periods
long l = between1.toTotalMonths();
System.out.println(l);
LocalDateTime date1 = LocalDateTime.of(2020, 12, 21, 11, 11, 11);
LocalDateTime date2 = LocalDateTime.of(2020, 12, 21, 12, 12, 12);
Duration duration = Duration.between(date1, date2);
System.out.println(duration);
//PT1H1M1S PT interval object 1H interval 1 hour 1M interval 1 minute 1S interval 1 second
long l = duration.toSeconds();
System.out.println(l);//3661 seconds between
long l1 = duration.toMillis();
System.out.println(l1);//3661000 milliseconds of interval
long l2 = duration.toNanos();
System.out.println(l2);//3661000000000 / / nanoseconds of interval10, JDK8 time class - Summary
JDK1.8 pre date function API
1 java.lang.System class
public static native long currentTimeMillis();
Used to return the time difference in milliseconds between the current time and 0:0:0 on January 1, 1970
2 java.util.Date class
Two constructors
new Date(); —> current time
new Date(Long milliseconds) - > creates a specified date based on the number of milliseconds
Use of two methods
toString() displays the current year, month, day, hour, minute and second
getTime() gets the corresponding number of milliseconds (timestamp) of the current date object
3 java.text.SimpleDateFormat class
The API of Date class is not easy to internationalize, and most of them are abandoned,
The SimpleDateFormat class is a concrete class that formats and parses time in a locale dependent manner
The format(Date d) method formats the time in a specific format
parse(String s) Method parses a string into time
4. Java.util.calendar Calendar Class
Get an instance of Calendar
An object that uses its subclass (GregorianCalendar)
Get the Calendar instance using Calendar.getInstance()
common method
1,set()
calendar.set(Calendar.DAY_OF_MONTH,22) - > set the date to the day of the month
2,get()
Calendar. Get (calendar. Day_of_month) ---- > the day of the month. The return value is int
calendar.get(Calendar.DAY_OF_YEAR) - > the day of the year
3,add()
Calendar. Add (calendar. Day_of_month, 3) - -- > add 3 days to the existing date
4,getTime()
calendar.getTime(); —> Return Date()
5,setTime()
calendar.setTime(new Date()) - > set the date to a certain date
JDK1.8 post date function API
Variability: classes such as date and time should be immutable, ---- > return a value, and the original object remains unchanged
Offset: the year in Date starts from 1900 and the month starts from 0
The date represents September 8, 2020 by subtracting new Date(2020-1900,9-1,8)
format; Formatting dates is only useful for Date, not Calendar
Thread is unsafe and cannot handle leap seconds, etc
Java8 absorbed the essence of Joda-Time(java date processing time library), opened the new API, and the new java.time contained the following classes.
Local datelocaldate
Local timelocaltime
Local datetime
Time zone ZonedDateTime
Durationjoda time
1. API for new date of jdk8
java.time - base package containing value objects
java.time.chrono - provides access to different calendar systems
java.time.format - format and parse time and date
Java.time.temporary - contains the underlying framework and extension features
java.time.zone - contains classes that support time zones
2 LocalDate,LocalTime,LocalDateTime
Get current time
LocalDate localDate = LocalDate.now(); // Mm / DD / yy`
LocalTime localTime = LocalTime.now(); // Day minute second
LocalDateTime localDateTime = LocalDateTime.now();
// LocalDateTime High frequency of use
// of() sets the specified month, day, hour, minute and second Reflect non offset
LocalDateTime dateTime = LocalDateTime.of(2019, 04, 10, 23, 03);
// plus Series Addition and subtraction of time
// Addition and subtraction of minus series time
// wiht series Set time
3 Instant time stamp Millisecond value between 00:00:00 on January 1, 1970 and a certain time
An instantaneous point on the timeline, which may be used to record the event timestamp of the application
The accuracy of Instant can reach nanosecond level
// Instant is very similar to java.util.Date
// Get the standard time of the prime meridian
Instant now = Instant.now();
System.out.println(now);
// Time of East eighth District Offset
OffsetDateTime offsetDateTime =now.atOffset(ZoneOffset.ofHours(8));
System.out.println(offsetDateTime);
// Milliseconds since January 1, 1970, 0:0:0(UTC)
long l = now.toEpochMilli();
System.out.println(l);
4. Java.time.format.datetimeformatter formats or parses time
Custom format
Datetimeformatter pattern = datetimeformatter. Ofpattern() ("yyyy MM DD HH: mm: SS") -- > is similar to SimpleDateFormat
5 Duration: Duration, used to calculate the interval between two "times"
Date interval: Period, used to calculate the interval between two dates
Application scenario
1. The LocalDate class uses an isLeapYear() method to return whether the year corresponding to the current LocalDate is a leap year
boolean leapYear = LocalDate.now().isLeapYear();
2 how to judge whether a date is before or after another date in java,
How to determine whether a date is before or after another date or equal,
In Java 8, isBefore() is used in the LocalDate class
isAfter() and equals() methods to compare the two dates.
If the date on which the method is called is earlier than the given date, the isBefore() method returns true
3 check whether the two dates are equal in Java 8
LocalDate overrides the equals method to compare dates
4 how to check repeated events, such as birthday, in Java 8
Another task related to time and date in java is to check for duplicate events, such as monthly bill day
How to judge whether it is a festival or repeated event in java, use the MonthDay class. This class is composed of month and day. It is not allowed Including year information,
It can be used to represent some dates or other combinations that occur repeatedly every year. Like other classes in the new date library, it is also non editable It is thread safe, and it is also a value class.
How to represent a fixed date, such as the expiration time of a credit card
Just as MonthDay represents a recurring day, YearMonth is another combination, which represents something like credit Card repayment date, time deposit maturity date,
options expiration date. You can use this class to find out how many days there are in this month,
The LengthOfMonth() method returns the number of days of the YearMonth instance, which is useful for checking whether February is 2 Month is very useful