Java.util.GregorianCalendar Java中的类

先决条件： Java.util.Locale、 Java.util.TimeZone、Calendar.get()
GregorianCalendar是Calendar的一个具体子类（实现了从接口或抽象类继承的所有成员），它实现了我们熟悉的最广泛使用的 Gregorian Calendar。

Java.util.GregorianCalendar 与Java.util.Calendar

GregorianCalendar和Calendar类之间的主要区别在于作为抽象类的Calendar类不能被实例化。所以Calendar类的一个对象被初始化为：

Calendar cal = Calendar.getInstance();

在这里，一个名为 cal 的Calendar类的对象被初始化为默认语言环境和时区中的当前日期和时间。而GregorianCalendar类是一个具体的类，可以被实例化。所以GregorianCalendar类的一个对象被初始化为：

GregorianCalendar gcal = new GregorianCalendar();

这里，一个名为GregorianCalendar类的 gcal 的对象被初始化为默认语言环境和时区中的当前日期和时间。
定义的字段：

GregorianCalendar Class defines two fields:
AD : referring to the common era(anno Domini)
BC : referring to before common era(Before Christ)

构造函数： GregorianCalendar对象有几个构造函数。从广义上讲， GregorianCalendar的构造函数要么在默认区域设置和/或时区中使用用户指定的日期和/或时间初始化对象，要么在用户指定的区域设置和/或时区中使用默认日期和时间初始化对象。这些如下：

Constructor Signature	Description
GregorianCalendar()	initializes the object with the current date and time in the default locale and time zone
GregorianCalendar(int year, int month, int dayOfMonth)	initializes the object with the date-set passed as parameters in the default locale and time zone
GregorianCalendar(int year, int month, int dayOfMonth, int hours, int minutes)	initializes the object with the date and time-set passed as parameters in the default locale and time zone
GregorianCalendar(int year, int month, int dayOfMonth, int hours, int minutes, int seconds)	initializes the object with the date and more specific time-set passed as parameters in the default locale and time zone
GregorianCalendar(Locale locale)	initializes the object with the current date and time in the default time zone and the locale passed as parameters
GregorianCalendar(TimeZone timeZone)	initializes the object with the current date and time in the default locale and the time zone passed as parameters
GregorianCalendar(TimeZone timeZone, Locale locale)	initializes the object with the current date and time in the locale and the time zone passed as parameters

JDK 8 中引入了from() 、 toZonedDateTime( ) 、 getCalendarType( )方法。

Java

// Java Program to show that Calendar class with
// default instantiation and GregorianCalendar class
// with default constructor is basically the same as both
// return the Gregorian Calendar for the default
// date, time, time zone and locale
 
import java.util.Calendar;
import java.util.GregorianCalendar;
 
class CalendarGFG {
    public static void main(String[] args)
    {
        // Creating an object of Calendar Class
        Calendar cal = Calendar.getInstance();
 
        /* Creating an object of
             GregorianCalendar Class */
        GregorianCalendar gcal = new GregorianCalendar();
 
        /* Displaying Current Date using
             Calendar Class */
        System.out.println("Calendar date: "
                           + cal.getTime());
 
        /* Displaying Current Date using
             GregorianCalendar Class */
        System.out.print("Gregorian date: "
                         + gcal.getTime());
    } // end of main function
} // end of class

输出：

Calendar date: Sat Apr 28 13:36:37 UTC 2018
Gregorian date: Sat Apr 28 13:36:37 UTC 2018

示例演示各种构造函数的用法：
1.使用默认构造函数

Java

// Java program to demonstrate simple GregorianCalendar
// operations
import java.util.Locale;
import java.util.TimeZone;
import java.util.Calendar;
import java.util.GregorianCalendar;
 
public class GregorianCalendarGFG {
    public static void main(String args[])
    {
        // declaring an array to store month abbreviations
        String month[] = { "Jan", "Feb", "Mar", "Apr",
                           "May", "Jun", "Jul", "Aug",
                           "Sep", "Oct", "Nov", "Dec" };
 
        // declaring an array to store AM or PM
        String amPm[] = { "AM", "PM" };
 
        /* Creating an object of GregorianCalendar class
             using default constructor*/
        GregorianCalendar gcal = new GregorianCalendar();
 
        // displaying the date, time, time zone and locale
        System.out.print("Date: "
                         + month[gcal.get(Calendar.MONTH)] + " "
                         + gcal.get(Calendar.DATE) + ", "
                         + gcal.get(Calendar.YEAR) + "\n"
                         + "Time: "
                         + gcal.get(Calendar.HOUR) + ":"
                         + gcal.get(Calendar.MINUTE) + ":"
                         + gcal.get(Calendar.SECOND) + " "
                         + amPm[gcal.get(Calendar.AM_PM)] + "\n"
                         + "Time Zone: " + gcal.getTimeZone().getDisplayName()
                         + "\n"
                         + "Locale: "
                         + Locale.getDefault().getDisplayName());
    } // end of main function
} // end of class

输出：

Date: Apr 30, 2018
Time: 10:21:51 PM
Time Zone: Coordinated Universal Time
Locale: English (United States)

2. 传递 year, month, dayOfMonth 作为参数：

Java

// Java program to demonstrate simple GregorianCalendar
// operations
import java.util.Locale;
import java.util.TimeZone;
import java.util.Calendar;
import java.util.GregorianCalendar;
 
public class GregorianCalendarGFG {
    public static void main(String args[])
    {
        // declaring an array to store month abbreviations
        String month[] = { "Jan", "Feb", "Mar", "Apr",
                           "May", "Jun", "Jul", "Aug",
                           "Sep", "Oct", "Nov", "Dec" };
 
        // declaring an array to store AM or PM
        String amPm[] = { "AM", "PM" };
 
        /* Creating an object of GregorianCalendar class
           by specifying year, month and dayOfMonth */
        GregorianCalendar gcal = new GregorianCalendar(2018, 3, 30);
 
        // displaying the date, time, time zone and locale
        System.out.print("Date: "
                         + month[gcal.get(Calendar.MONTH)] + " "
                         + gcal.get(Calendar.DATE) + ", "
                         + gcal.get(Calendar.YEAR) + "\n"
                         + "Time: "
                         + gcal.get(Calendar.HOUR) + ":"
                         + gcal.get(Calendar.MINUTE) + ":"
                         + gcal.get(Calendar.SECOND) + " "
                         + amPm[gcal.get(Calendar.AM_PM)] + "\n"
                         + "Time Zone: " + gcal.getTimeZone().getDisplayName()
                         + "\n"
                         + "Locale: "
                         + Locale.getDefault().getDisplayName());
    } // end of main function
} // end of class

输出：

Date: Apr 30, 2018
Time: 0:0:0 AM
Time Zone: Coordinated Universal Time
Locale: English (United States)

3. 通过年、月、dayOfMonth、hourOfDay、minute：

Java

// Java program to demonstrate simple GregorianCalendar
// operations
import java.util.Locale;
import java.util.TimeZone;
import java.util.Calendar;
import java.util.GregorianCalendar;
 
public class GregorianCalendarGFG {
    public static void main(String args[])
    {
        // declaring an array to store month abbreviations
        String month[] = { "Jan", "Feb", "Mar", "Apr",
                           "May", "Jun", "Jul", "Aug",
                           "Sep", "Oct", "Nov", "Dec" };
 
        // declaring an array to store AM or PM
        String amPm[] = { "AM", "PM" };
 
        /* Creating an object of GregorianCalendar class
           by specifying year, month, dayOfMonth,
           hourOfDay and minute */
        GregorianCalendar gcal = new GregorianCalendar(2018, 3, 30, 10, 21);
 
        // displaying the date, time, time zone and locale
        System.out.print("Date: "
                         + month[gcal.get(Calendar.MONTH)] + " "
                         + gcal.get(Calendar.DATE) + ", "
                         + gcal.get(Calendar.YEAR) + "\n"
                         + "Time: "
                         + gcal.get(Calendar.HOUR) + ":"
                         + gcal.get(Calendar.MINUTE) + ":"
                         + gcal.get(Calendar.SECOND) + " "
                         + amPm[gcal.get(Calendar.AM_PM)] + "\n"
                         + "Time Zone: " + gcal.getTimeZone().getDisplayName()
                         + "\n"
                         + "Locale: "
                         + Locale.getDefault().getDisplayName());
    } // end of main function
} // end of class

输出：

Date: Apr 30, 2018
Time: 10:21:0 AM
Time Zone: Coordinated Universal Time
Locale: English (United States)

4. 通过年、月、dayOfMonth、hourOfDay、分、秒：

Java

// Java program to demonstrate simple GregorianCalendar
// operations
import java.util.Locale;
import java.util.TimeZone;
import java.util.Calendar;
import java.util.GregorianCalendar;
 
public class GregorianCalendarGFG {
    public static void main(String args[])
    {
        // declaring an array to store month abbreviations
        String month[] = { "Jan", "Feb", "Mar", "Apr",
                           "May", "Jun", "Jul", "Aug",
                           "Sep", "Oct", "Nov", "Dec" };
 
        // declaring an array to store AM or PM
        String amPm[] = { "AM", "PM" };
 
        /* Creating an object of GregorianCalendar class
           by specifying year, month, dayOfMonth,
           hourOfDay, minute and second */
        GregorianCalendar gcal = new GregorianCalendar(2018, 3, 30, 10, 21, 51);
 
        // displaying the date, time, time zone and locale
        System.out.print("Date: "
                         + month[gcal.get(Calendar.MONTH)] + " "
                         + gcal.get(Calendar.DATE) + ", "
                         + gcal.get(Calendar.YEAR) + "\n"
                         + "Time: "
                         + gcal.get(Calendar.HOUR) + ":"
                         + gcal.get(Calendar.MINUTE) + ":"
                         + gcal.get(Calendar.SECOND) + " "
                         + amPm[gcal.get(Calendar.AM_PM)] + "\n"
                         + "Time Zone: " + gcal.getTimeZone().getDisplayName()
                         + "\n"
                         + "Locale: "
                         + Locale.getDefault().getDisplayName());
    } // end of main function
} // end of class

输出：

Date: Apr 30, 2018
Time: 10:21:51 AM
Time Zone: Coordinated Universal Time
Locale: English (United States)

5. 通过传递 timeZone 作为参数：

Java

// Java program to demonstrate simple GregorianCalendar
// operations
import java.util.TimeZone;
import java.util.Locale;
import java.util.Calendar;
import java.util.GregorianCalendar;
 
public class GregorianCalendarTest {
    public static void main(String args[])
    {
        // declaring an array to store month abbreviations
        String month[] = { "Jan", "Feb", "Mar", "Apr",
                           "May", "Jun", "Jul", "Aug",
                           "Sep", "Oct", "Nov", "Dec" };
 
        // declaring an array to store AM or PM
        String amPm[] = { "AM", "PM" };
 
        /* Creating an object of TimeZone class to create
             an object of GregorianCalendar class to assign
             an user defined time zone (GMT + 5:30)*/
        TimeZone tz = TimeZone.getTimeZone("GMT+5:30");
        GregorianCalendar gcal = new GregorianCalendar(tz);
 
        // displaying the date, time, time zone and locale
        System.out.print("Date: "
                         + month[gcal.get(Calendar.MONTH)] + " "
                         + gcal.get(Calendar.DATE) + ", "
                         + gcal.get(Calendar.YEAR) + "\n"
                         + "Time: "
                         + gcal.get(Calendar.HOUR) + ":"
                         + gcal.get(Calendar.MINUTE) + ":"
                         + gcal.get(Calendar.SECOND) + " "
                         + amPm[gcal.get(Calendar.AM_PM)] + "\n"
                         + "Time Zone: " + gcal.getTimeZone().getDisplayName()
                         + "\n"
                         + "Locale: " + Locale.getDefault().getDisplayCountry());
    } // end of main function
} // end of class

输出：

Date: May 1, 2018
Time: 4:24:7 AM
Time Zone: GMT+05:30
Locale: United States

6. 通过将语言环境作为参数传递：

Java

// Java program to demonstrate simple GregorianCalendar
// operations
import java.util.TimeZone;
import java.util.Locale;
import java.util.Calendar;
import java.util.GregorianCalendar;
 
public class GregorianCalendarTest {
    public static void main(String args[])
    {
        // declaring an array to store month abbreviations
        String month[] = { "Jan", "Feb", "Mar", "Apr",
                           "May", "Jun", "Jul", "Aug",
                           "Sep", "Oct", "Nov", "Dec" };
 
        // declaring an array to store AM or PM
        String amPm[] = { "AM", "PM" };
 
        /* Creating an object of Locale class to create
             an object of GregorianCalendar class to assign
             an user defined locale (India)*/
        Locale l = new Locale("en", "IN");
        GregorianCalendar gcal = new GregorianCalendar(l);
 
        // displaying the date, time, time zone and locale
        System.out.print("Date: "
                         + month[gcal.get(Calendar.MONTH)] + " "
                         + gcal.get(Calendar.DATE) + ", "
                         + gcal.get(Calendar.YEAR) + "\n"
                         + "Time: "
                         + gcal.get(Calendar.HOUR) + ":"
                         + gcal.get(Calendar.MINUTE) + ":"
                         + gcal.get(Calendar.SECOND) + " "
                         + amPm[gcal.get(Calendar.AM_PM)] + "\n"
                         + "Time Zone: "
                         + gcal.getTimeZone().getDisplayName()
                         + "\n"
                         + "Locale: " + l.getDisplayCountry());
    } // end of main function
} // end of class

输出：

Date: Apr 30, 2018
Time: 10:58:30 PM
Time Zone: Coordinated Universal Time
Locale: India

7. 通过传递 timeZone 和 locale 作为参数：

Java

// Java program to demonstrate simple GregorianCalendar
// operations
import java.util.TimeZone;
import java.util.Locale;
import java.util.Calendar;
import java.util.GregorianCalendar;
 
public class GregorianCalendarTest {
    public static void main(String args[])
    {
        // declaring an array to store month abbreviations
        String month[] = { "Jan", "Feb", "Mar", "Apr",
                           "May", "Jun", "Jul", "Aug",
                           "Sep", "Oct", "Nov", "Dec" };
 
        // declaring an array to store AM or PM
        String amPm[] = { "AM", "PM" };
 
        /* Creating an object of TimeZone class and Locale
             class to create an object of GregorianCalendar
             class to assign an user defined time zone
             (GMT + 5:30) and locale (India)*/
        TimeZone tz = TimeZone.getTimeZone("GMT+5:30");
        Locale l = new Locale("en", "IN");
        GregorianCalendar gcal = new GregorianCalendar(tz, l);
 
        // displaying the date, time, time zone and locale
        System.out.print("Date: "
                         + month[gcal.get(Calendar.MONTH)] + " "
                         + gcal.get(Calendar.DATE) + ", "
                         + gcal.get(Calendar.YEAR) + "\n"
                         + "Time: "
                         + gcal.get(Calendar.HOUR) + ":"
                         + gcal.get(Calendar.MINUTE) + ":"
                         + gcal.get(Calendar.SECOND) + " "
                         + amPm[gcal.get(Calendar.AM_PM)] + "\n"
                         + "Time Zone: "
                         + gcal.getTimeZone().getDisplayName()
                         + "\n"
                         + "Locale: " + l.getDisplayCountry());
    } // end of main function
} // end of class

输出：

Date: May 1, 2018
Time: 4:34:59 AM
Time Zone: GMT+05:30
Locale: India

参考：
GregorianCalendar (Java Platform SE 8) – Oracle 帮助中心