Common API of the Java Date class Introduction

Data class

java.util.Date: indicates the date and time of the class
class Date represents a specific moment, with millisecond precision.
Ms: millisecond 1000 msec = 1 sec

The date is converted into milliseconds:

The current date: 2019-07-18
Time origin (0 ms): 1970-01-01 00:00:00 (Greenwich)
Is to calculate the current date to the time between the origin experienced a total of how many milliseconds

Note:
China belongs to the East eight districts, the time will increase 8 hours

1970-01-01 08：00：00

Converting milliseconds Date:

1 day = 24 * 60 * 60 = 86,400 seconds = 86400 * 1000 = 86400000 ms

use:

Date class configuration parameters methods 
Date DATE = new new Date (); 
Date (); // Get current system time and date 
--------- 
Date DATE = new new Date (0L );  Date (Long DATE ); // pass milliseconds, the conversion of milliseconds to a date date  -----------  date dATE = new new date (); Long Time = date.getTime (); Long the getTime () converts the date to milliseconds (equivalent to System.currentTimeMillis () method) returns the number of milliseconds since January 1, 1970 00-00-00GMT this Date object represents.

DateFormat class

java.text.DateFormat: a date / time formatting subclasses of abstract classes

effect:

Format (that is, the date -> text), parsing (text -> date)

Member method:

String format (Date date) according to the designated mode, the date Date, formatted to conform to the pattern string
Date parse (String source) to conform to the schema string, resolves to Date Date
DateFormat class is an abstract class, you can not directly create objects to use, you can use a subclass of DateFormat class

java.text.SimpleDateFormat extends DateFormat

The DateFormat class method format, the text is formatted date

Steps for usage:

Create simpleDateFormat object constructor transmission mode specified
The method of calling format SimpleDateFormat object, the method specified in the configuration mode, the mode Date date formatted to conform to a string (text)

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒");
Date date = new Date();
String d = sdf.format(date);

Class Calendar

Description:
java.util.Calendar class; calendar class

Calendar class is an abstract class, a method of operating inside it provides many calendar field (YEAR, MONTH, DAY_OF_MONTH, HOUR )
Calendar class can not be used directly to create objects, inside there is a static method called getInstance (), which returns a subclass object class Calendar
When static Calendar getInstance () uses the default time zone and locale to get a calendar.

Calendar c = Calendar.getInstance (); // Polymorphic

Calendar class of common member method:

public int get (int field); Returns the value of a given calendar field.
public void set (int field, int value); given calendar field to the given value
public abstract void add (int field, int amount); According to the rules of the calendar, add or subtract an amount of time specified for the given calendar field.
public Data getTime (); return a time value times Calendar Date object (from epoch to millisecond offset) FIG.

// public int get (int field) ; return value of a given calendar field. 
C = Calendar Calendar.getInstance (); 
int year = c.get (Calendar.YEAR); 
int = month The c.get (the Calendar.MONTH); 

/// public void SET (Field int, int value); given the calendar field to the given value 
// set the year 9999 
// set the month September 
c.set (Calendar.YEAR, 9999 );  c.set (of the Calendar.MONTH, 9 ); 
 // increase in  c.add (Calendar.YEAR, 2 ); // the calendar object, the object into a date date date = c.getTime ();