Java Time Class

First, Date class

Date: Represents a specific moment, accurate to milliseconds
Construction Method:
(1) Public date (): Creates a Date object based on the current default millisecond value
(2) Public date (long date): Creates a Date object based on the given millisecond value
Member Methods:
(1) public long getTime (): Gets the time that returns the number of milliseconds that this Date object represents since January 1, 1970 00:00:00 GMT.
(2) Public long settime (long): Sets the time that represents the point in time milliseconds after January 1, 1970 00:00:00 GMT.
Note: General acquisition time, we are more commonly used: System.currenttimemillis () method.

what the date class needs to know :
1. Get a millisecond value from date
GetTime ()
2. Convert a millisecond value to date
A: Construction Method implementation: Public date (long date)
B: Member method implementation: Public long settime (long time)

Second, DateFormat class

in program development
String ———————— > Date
Date Control Transformation Database
Date ———————— > String
DateFormat class: Date/Time format subclass abstract class, we use specific subclasses: SimpleDateFormat
member Methods:
1. Format:date--> String
Public final String format (date date)
2. Parsing:string--> Date
Public Date Parse (String source)
the specific implementation class of the DateFormat class: SimpleDateFormat
the construction method of SimpleDateFormat class：
(1) SimpleDateFormat (): Default date/Time mode
(2) SimpleDateFormat (String pattern): Given date/time pattern
Date/Time mode:
Year Y
Month M
Day D
Hours H
Min m
Seconds s

Date--String: Formatting
Create Date Object
Date d = new Date ();
Creating a formatted Object
First type: default date/Time mode
SimpleDateFormat SDF = new SimpleDateFormat ();
Public final String format (date date)
String s = sdf.format (d);
System.out.println (s);
Second type: given date/time pattern
SimpleDateFormat SDF = new SimpleDateFormat ("yyyy mm month DD Day HH:mm:ss");
Public final String format (date date)
String s = sdf.format (d);
System.out.println (s);
String--Date: Parse
String str = "2016-09-30 19:29:30";
Note: The string format must match the given string format when parsing the string to a date
SimpleDateFormat sdf2 = new SimpleDateFormat ("Yyyy-mm-dd HH:mm:ss");
Date dd = sdf2.parse (str);
SYSTEM.OUT.PRINTLN (DD);

Case : custom encapsulation, date and string conversion of tool classes to each other
Import java.text.ParseException;
Import Java.text.SimpleDateFormat;
Import Java.util.Date;

/**
* Tool class for converting dates and strings to each other
* @author
*/
public class Dateutil {
Private Dateutil () {
}

           /**
            * Method: Turn a Date object into a string
&N Bsp           * @param d formatted Date object
            * @param format passed over Format to be converted
            * @return formatted string
            */
            public static string datetostring (Date D, string format) {
    &NB Sp            //SimpleDateFormat SDF = new SimpleDateFormat (format);
                 //return Sdf.format (d);
                  return new SimpleDateFormat (format). Format (d);
           }

/**
* Method Function: Parse a string into a Date object
* @param s parsed string
* @param format to be converted
* @return The parsed Date object
* @throws ParseException
*/
public static Date Stringtodate (string s, string format) throws ParseException {
return new SimpleDateFormat (format). Parse (s);
}
}

Third, Calender class

Calendar class : An abstract class that provides methods for converting a specific moment to a group of calendar fields such as year, MONTH, Day_of_month, HOUR, and provides methods for manipulating calendar fields, such as getting the date of the next week.
Calendar field:
(1) public static final int year: Indicates the year's Get and set field numbers, indicating years.
(2) public static final int month: A field number that indicates the get and set of the month, indicating the month of the year.
(3) public static final int date:get and set field numbers indicating the day of the one month.
(4) public static final int hour_of_day:get and set field numbers indicating the hour of the day.
(5) public static final int Minute:get and set number of fields indicating the minute of the hour.
(6) public static final int second:get and set field numbers, indicating the seconds in a minute.
(7) public static final int Day_of_year:get and set number of fields indicating the number of days in the current year.
(8) public static final int day_of_month:get and set field numbers indicating the day of the one month.
(9) public static final int day_of_week:get and set field numbers indicating the day of the one week. The values for this field are SUNDAY, MONDAY, Tuesday, Wednesday, Thursday, FRIDAY, and SATURDAY.

Common methods:

(1) public static calendar getinstance (): Get a calendar using the default time zone and locale
such as: Calendar RightNow = Calendar.getinstance ();
(2) public int get (int field): Returns the value of the given Calendar field. Each calendar field in the Calendar class is a static member variable and is of type int.
Get year
int year = Rightnow.get (calendar.year);
Get month
int month = Rightnow.get (calendar.month);
Get Day
int date = Rightnow.get (calendar.date);
SYSTEM.OUT.PRINTLN (Year + "years" + (month + 1) + "Month" + Date + "Day");
(3) public void Add (int field,int amount): Operates on the current calendar based on the given calendar field and the corresponding time.
5 years later, 10 days ago
C.add (Calendar.year, 5);
C.add (Calendar.date,-10);
(4) Public final void set (int year,int month,int date): Sets the month and day of the current calendar
C.set (2016, 10, 30);///NOTE: The month is counted starting from 0
Case：get how many days in February of any year
Analysis:
A: Keyboard entry for any year
B: Set Calendar object's Month day
Year: a input data
Month: 2
Day: 1
C: Push the time forward one day, the last day of February
D: Get this day output
Code implementation:
Scanner sc = new Scanner (system.in);
System.out.println ("Please enter the Year:");
int year = Sc.nextint ();
Calendar C = calendar.getinstance ();
C.set (year, 2, 1);
C.add (Calendar.date,-1);
System.out.println (C.get (calendar.date));

expansion : publicstatic Calendar getinstance () method design idea Expansion
The idea of this approach:
Abstract class Person {
public static Person Getperson () {
return new Student ();
}
}
Class Student extends Person {
}

Java Time Class