The new date and time API

Legacy API defect

　　1. Design Defect: Calendar class such as the month is counted from 0

　　　  2. Non-thread-safe: java.util.Date non-thread-safe, all the dates are variable class

　　　  3. Time zone trouble handling: Date class does not offer international, no time zone support, so the introduction of the Java class java.util.Calendar and java.util.TimeZone, but above all their problems also exist

The new API

　　1.localdat to, localtime

　　　　LocalDate: instances of the class is an immutable object, it only provides a simple date, time does not include the information of the day, it does not carry any information related to the time zone. LocalDate can create an instance of (y, m, d) by the static method, may be () Gets the current date by now.

　　　　LocalTime: time of day, such as 8:55:13, can be expressed LocalTime. LocalTime may be used to create instances of method overloading of the plant

　　　　LocalDateTime: LocalDate and LocalTime is fit, also said the date and time, but with no time zone information

　　　　Code Example:

package Date;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Month;

public  class the Test {
     public  static  void main (String [] args) {
         // get the current date and time 
        the LocalDateTime = currentTime LocalDateTime.now ();
        System.out.println ( "Current Time:" + currentTime);

        LocalDate date1 = currentTime.toLocalDate();
        System.out.println("date1: " + date1);

        Month month = currentTime.getMonth();
        int day = currentTime.getDayOfMonth();
        int seconds = currentTime.getSecond();

        System.out.println("月: " + month + ", 日: " + day + ", 秒: " + seconds);

        LocalDateTime date2 = currentTime.withDayOfMonth(10).withYear(2012);
        System.out.println("date2: " + date2);

        // 12 december 2014
        LocalDate date3 = LocalDate.of(2014, Month.DECEMBER, 12);
        System.out.println("date3: " + date3);

        @ 22 hours 15 minutes 
        LocalTime date4 = LocalTime.of (22 is, 15 );
        System.out.println("date4: " + date4);

        // parse the string 
        LocalTime date5 = LocalTime.parse ( "20:15:30" );
        System.out.println("date5: " + date5);
    }
}

View Code

 

　　　2. manipulation, parsing and formatting date

　　　　All dates and times are to achieve a Temporal Object Interface, static or instance method creates a copy of an object without modifying the original object. Common methods are as follows:

Method name	Whether it is a static method	description
from	Yes	Create an object instance of the object passed in Temporal
now	Yes	Temporal create objects based on the system clock
of	Yes	The object is created by an armed Temporal instance of an object
parents	Yes	Temporal objects created by the string instance
atOffset	no	The Temporal objects and a combination of the time zone offset
atZone	no	The Temporal objects and a combination of time zone
format	no	Temporal format used to convert the object to a string
get	no	Temporal value read for a part of the object
minus	no	The copy is created by the current value of the Temporal object minus a certain length of time
plus	no	Plus a certain length of time to create the copy by the current value of the Temporal object
with	no	The Temporal objects to create the object as a template for some state modified copy

　　  3. Use TemporalAdjuster.

　　　　It can be used with heavy-duty version of the method, passing it provides a more customized selection of TemporalAdjuster object.

package Date;

import java.time.DayOfWeek;
import java.time.LocalDateTime;
import java.time.temporal.TemporalAdjusters;

public  class TemporalAdjustersTest {
     public  static  void main (String [] args) {
         // Current time: 2020-02-21T16: 32: 01.492 
        the LocalDateTime = currentTime LocalDateTime.now ();
        System.out.println ( "Current Time:" + currentTime);

        // nextDay: 2020-02-23T16: 32: 01.492 create a new date, and set its value to adjust the date, first date a few weeks in line with the requirements specified. If the date has been met, the object is returned directly 
        the LocalDateTime nextDay = currentTime.with (TemporalAdjusters.nextOrSame (DayOfWeek.SUNDAY));
        System.out.println("nextDay: " + nextDay);
        
        // firstDay: 2020-02-01T16: 37 [: 38.789 create a date, it is the first day of the month 
        the LocalDateTime firstDay = currentTime.with (TemporalAdjusters.firstDayOfMonth ());
        System.out.println("firstDay: " + firstDay);
    }
}