Java GregorianCalendar Class

GregorianCalendar is a calendar class in Java that represents the Gregorian calendar, inheriting from the Calendar class. This class provides the standard calendar system used by most countries in the world.

The GregorianCalendar class is located in the java.util package and is used for date and time related operations. It supports date calculations from year 1 AD to the future, and takes into account complex calendar rules such as leap years.

Basic Usage of GregorianCalendar

Creating a GregorianCalendar Instance

There are several ways to create a GregorianCalendar instance:

Example

// Create an instance representing the current date and time
GregorianCalendar calendar1 = new GregorianCalendar();

// Create an instance with the specified year, month, and date
// Note: months start from 0, 0 represents January
GregorianCalendar calendar2 = new GregorianCalendar(2023, 10, 15);

// Create an instance with the specified year, month, date, hour, and minute
GregorianCalendar calendar3 = new GregorianCalendar(2023, 10, 15, 14, 30);

// Create an instance with the specified year, month, date, hour, minute, and second
GregorianCalendar calendar4 = new GregorianCalendar(2023, 10, 15, 14, 30, 45);

Getting Date and Time Information

Example

GregorianCalendar calendar = new GregorianCalendar();

int year = calendar.get(Calendar.YEAR);       // Get the year
int month = calendar.get(Calendar.MONTH);    // Get the month (0-11)
int day = calendar.get(Calendar.DAY_OF_MONTH); // Get the date
int hour = calendar.get(Calendar.HOUR_OF_DAY); // Get the hour (24-hour format)
int minute = calendar.get(Calendar.MINUTE);   // Get the minute
int second = calendar.get(Calendar.SECOND);   // Get the second

Setting Date and Time

Example

GregorianCalendar calendar = new GregorianCalendar();

// Set the year
calendar.set(Calendar.YEAR, 2024);

// Set the month (0-11)
calendar.set(Calendar.MONTH, Calendar.JANUARY);

// Set the date
calendar.set(Calendar.DAY_OF_MONTH, 1);

// Set year, month, and day simultaneously
calendar.set(2024, Calendar.JANUARY, 1);

Common Methods of GregorianCalendar

Date Calculation

Example

GregorianCalendar calendar = new GregorianCalendar(2023, Calendar.NOVEMBER, 15);

// Add 10 days
calendar.add(Calendar.DAY_OF_MONTH, 10);

// Subtract 2 months
calendar.add(Calendar.MONTH, -2);

Comparing Dates

Example

GregorianCalendar cal1 = new GregorianCalendar(2023, Calendar.NOVEMBER, 15);
GregorianCalendar cal2 = new GregorianCalendar(2023, Calendar.DECEMBER, 25);

// Compare two dates
int result = cal1.compareTo(cal2);  // Returns a negative number if cal1 is before cal2, a positive number if after, and 0 if equal

// Check if it is before a certain date
boolean isBefore = cal1.before(cal2);

// Check if it is after a certain date
boolean isAfter = cal1.after(cal2);

Checking for Leap Year

Example

// Check whether the specified year is a leap year
boolean isLeapYear = new GregorianCalendar().isLeapYear(2024);

Converting to Date Object

Example

GregorianCalendar calendar = new GregorianCalendar();
Date date = calendar.getTime();

Setting from Date Object

Example

Date date = new Date();
GregorianCalendar calendar = new GregorianCalendar();
calendar.setTime(date);

Date Formatting Output

GregorianCalendar itself does not provide formatting methods, but it can be used together with SimpleDateFormat:

Example

GregorianCalendar calendar = new GregorianCalendar(2023, Calendar.NOVEMBER, 15, 14, 30);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String formattedDate = sdf.format(calendar.getTime());
System.out.println(formattedDate);  // Output: 2023-11-15 14:30:00

Notes

Months Start from 0

In GregorianCalendar, months start from 0, where 0 represents January and 11 represents December. For better code readability, it is recommended to use the constants defined in the Calendar class:

Example

// Not recommended
new GregorianCalendar(2023, 10, 15);

// Recommended
new GregorianCalendar(2023, Calendar.NOVEMBER, 15);

Thread Safety

GregorianCalendar is not thread-safe. If it needs to be used in a multi-threaded environment, synchronization should be performed or separate instances should be created for each thread.

Alternatives

In Java 8 and above, it is recommended to use the new date and time API (classes in the java.time package), such as LocalDate, LocalDateTime, etc. They have a more reasonable design and are more convenient to use.

Complete Example

Example

import java.util.GregorianCalendar;
import java.util.Calendar;
import java.text.SimpleDateFormat;

public class GregorianCalendarExample {
    public static void main(String[] args) {
        // Create an instance of the current date
        GregorianCalendar calendar = new GregorianCalendar();
       
        // Display the current date and time
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        System.out.println("Current time: " + sdf.format(calendar.getTime()));
       
        // Check if this year is a leap year
        int year = calendar.get(Calendar.YEAR);
        boolean isLeap = calendar.isLeapYear(year);
        System.out.println(year + "year " + (isLeap ? " is" : " is not") + "a leap year");
       
        // Add 30 days
        calendar.add(Calendar.DAY_OF_MONTH, 30);
        System.out.println("30 days later: " + sdf.format(calendar.getTime()));
       
        // Create an instance of a specific date
        GregorianCalendar birthday = new GregorianCalendar(1990, Calendar.JULY, 15);
        System.out.println("Birthday: " + sdf.format(birthday.getTime()));
    }
}

The output result is:

当前时间: 2025-05-01 11:37:43
2025年不是闰年
30天后: 2025-05-31 11:37:43
生日: 1990-07-15 00:00:00

Method Summary

GregorianCalendar is a concrete implementation class of Calendar. The following are its commonly used methods:

Constructors

Method Description
GregorianCalendar() Creates an object using the default time zone and locale
GregorianCalendar(int year, int month, int dayOfMonth) Creates an object with the specified year, month, and day
GregorianCalendar(int year, int month, int dayOfMonth, int hourOfDay, int minute) Creates an object with the specified year, month, day, hour, and minute
GregorianCalendar(int year, int month, int dayOfMonth, int hourOfDay, int minute, int second) Creates an object with the specified year, month, day, hour, minute, and second
GregorianCalendar(Locale locale) Creates an object using the default time zone and the specified locale
GregorianCalendar(TimeZone zone) Creates an object using the specified time zone and the default locale
GregorianCalendar(TimeZone zone, Locale locale) Creates an object using the specified time zone and locale

Specific Methods

Method Description
boolean isLeapYear(int year) Determines whether the specified year is a leap year
void setGregorianChange(Date date) Sets the conversion date from the Julian calendar to the Gregorian calendar
Date getGregorianChange() Gets the conversion date from the Julian calendar to the Gregorian calendar

Common Methods Inherited from Calendar

Method Description
int get(int field) Gets the value of the specified field
void set(int field, int value) Sets the value of the specified field
void add(int field, int amount) Adds or subtracts the specified amount of time
void roll(int field, int amount) Adds or subtracts time without changing larger fields
boolean after(Object when) Determines whether it is after the specified time
boolean before(Object when) Determines whether it is before the specified time
long getTimeInMillis() Returns the time value (milliseconds)
void setTimeInMillis(long millis) Sets the Calendar with a millisecond time value
Date getTime() Returns the corresponding Date object
void setTime(Date date) Sets the time using a Date object

Field Constants (Inherited from Calendar)

Field Description
YEAR Year field
MONTH Month field (0-11)
DATE / DAY_OF_MONTH Day of the month
DAY_OF_WEEK Day of the week (1-7, 1=Sunday)
HOUR Hour in 12-hour format
HOUR_OF_DAY Hour in 24-hour format
MINUTE Minute
SECOND second
MILLISECOND Millisecond
AM_PM AM or PM
Other Extensions