Java Date and Time – GregorianCalendar Class with Example

The definition of an efficient programming language depends on how well it can handle dates and Time. Java provides us with built-in classes like Date and Calendar to handle operations related to date and time. In this article, we will discuss at length how these classes and their methods can be implemented into a Java program.

The Date class in Java

The java.util package in Java contains many utilities that are very important for a program. One such class is the Date class. This class deals with operations related to date and time. This class implements the Cloneable, Serializable, and Comparable interfaces of Java.

Java Date class constructors

The Date class consists of six Java constructors, but only two of them are in use; the other four are deprecated.

1. Date()

This is the default constructor of the Date class. It is used to initialize the Date class objects with the present date and time.

2. Date(long millisecond)

It is a parameterized constructor of the Date class. The argument passed is in the form of milliseconds. It initializes the object with the total milliseconds that have passed since midnight, January 1, 1970.

Java Date class Methods

Getting Current Date and Time

We will use two techniques to get the current date and time of our system.
1. Using the Date class
2. Using the Calendar class

1. Using the Date class in Java

In this method, we will create an object of the Date class and then call the toString() method using the object to get the present date and time of the system.

Code to get the current date and time using the Date Class:

package com.DataFlair.DateAndTime;
import java.util.Date;
public class CurrDateUsingDateClass
{
      public static void main(String args[]) {
      Date date = new Date();
      System.out.println(date.toString());
   }
}

The output of the above code:

2. Using Calendar Class

We will use the getInstance() method of the Calendar class to create an instance, and use it to call the getTime() method to get the current time of the system.

Code to get the current date and time using the Calendar Class:

package com.DataFlair.DateAndTime;
import java.util.Calendar;
public class CurrDateUsingCalenderClass
{
    public static void main(String args[]) 
    {
        Calendar current = Calendar.getInstance();
        System.out.println(current.getTime());
    }
}

The output of the above code is:

Comparison of Date

We can compare two dates in three ways:

• Using the getTime() function to get the number of milliseconds since January 1, 1970, for both dates, and then comparing the two values.
• Using the before(), after(), and equals() methods to compare the boolean values returned by the methods.
• There is also the compareTo() method, which can be used to compare two dates. It returns 0, negative, and positive values, depending on the dates compared.

Formatting Date Using the SimpleDateFormat class

We can format dates using the concrete class called SimpleDateFormat. We can start by choosing any user-defined pattern for date formatting.

Code to understand the use of SimpleDateFormat:

package com.DataFlair.DateAndTime;
import java.util.*;
import java.text.*;
public class DateFormatting
{
    public static void main(String args[]) 
   {
      Date CurrDate = new Date( );
      SimpleDateFormat formatDate = new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
      System.out.println("Current Date(Formatted): " + formatDate.format(CurrDate));
   }
}

The output of the above code:

SimpleDateFormat formatting codes

In the above program, we used codes like E, yyyy, etc. These codes are all specific pattern codes defined inside the SimpleDateFormat. Let us discuss all the codes through the table below.

Characters to convert Java Date and Time

Date formatting Using printf

The above characters can be used easily to format a date using the printf method. We just have to give a two-letter format starting with t and any of the above characters.

Code to understand the implementation of printf:

package com.DataFlair.DateAndTime;
import java.util.Date;
public class DateFormattingusingPrintf
{
    public static void main(String args[]) 
    {
      Date date = new Date();
      String str = String.format("Current Date/Time of the system : %tc", date );
      System.out.printf(str);
   }
}

The output of the above code:

We can apply multiple formatting at the same time as well. We just have to give % before every character and terminate with $

Code to implement multiple formatting using printf:

package com.DataFlair.DateAndTime;
import java.util.Date;
public class DateFormattingusingPrintf
{
    public static void main(String args[]) 
    {
      Date date_of_system = new Date();
      System.out.printf("%1$s %2$tB %2$td, %2$tY", "Current date of the system:", date_of_system);
   }
}

The output of the above code:

We can also use < flag to indicate that the same argument as the preceding should be used again.

Code to understand flag in printf:

package com.DataFlair.DateAndTime;
import java.util.Date;
public class DateFormattingusingPrintf
{
    public static void main(String args[]) 
    {
      Date date = new Date();
      System.out.printf("%s %tB %<te, %<tY", "Current date of the system:", date);
   }
}

The output of the above code:

Parsing strings into dates

The SimpleDateFormat has a method called parse() which tries to parse a string according to the format stored in the given SimpleDateFormat object.

Code to understand the parse method:

package com.DataFlair.DateAndTime;
import java.util.*;
import java.text.*;
public class parseDate
{
     public static void main(String args[]) {
      SimpleDateFormat formatofDate = new SimpleDateFormat ("yyyy-MM-dd"); 
      String input = args.length == 0 ? "2021-08-19" : args[0]; 
      System.out.print(input + " is Parsed as "); 
      Date t;
      try {
         t = formatofDate.parse(input); 
         System.out.println(t); 
      } catch (ParseException e) { 
         System.out.println("The string is unparseable " + formatofDate); 
      }
   }
}

The output of the above code:

Making the program sleep for a while

We can make a program sleep for any period of time from one millisecond up to the lifetime of our computer.

Code to make our system sleep for 6 seconds:

package com.DataFlair.DateAndTime;
import java.util.*;
public class Sleeping
{
   public static void main(String args[]) {
      try { 
         System.out.println(new Date( ) + "\n"); 
         Thread.sleep(10*60*10); 
         System.out.println(new Date( ) + "\n"); 
      } catch (Exception e) {
         System.out.println("Got an exception!"); 
      }
   }
}

The output of the above code:

Now let us try to calculate the time for which our program slept.

Code to calculate the time for which our program sleeps:

package com.DataFlair.DateAndTime;
import java.util.*;
public class Sleeping
{
     public static void main(String args[]) {
      try {
         long start = System.currentTimeMillis( );
         System.out.println(new Date( ) + "\n");
         Thread.sleep(10*60*10);
         System.out.println(new Date( ) + "\n");
         long end = System.currentTimeMillis( );
         long diff = end - start;
         System.out.println("Difference is : " + diff);
      } catch (Exception e) {
         System.out.println("Got an exception!");
      }
   }
}

The output of the above code:

GregorianCalendar Class

Another concrete implementation of the calendar class is the GregorianCalendar class. It implements the normal Gregorian Calendar. We can instantiate the GregorianCalendar class using the getInstance() method. It can define two fields: AD(Anno Domini)and BC(Before Christ).

There are several constructors in the GregorianCalendar class:
1. GregorianCalendar(): It is the default constructor of the GregorianCalendar class. The default constructor constructs a default calendar using the current time in the default time zone with the default location.

2. GregorianCalendar(int year, int month, int date): It is a parameterized constructor of the GregorianCalendar class that constructs a GregorianCalendar with the mentioned date in the default time zone with the default location.

3. GregorianCalendar(int year, int month, int date, int hour, int minute): It is a parameterized constructor of the GregorianCalendar class that constructs a GregorianCalendar with the mentioned date and time in the default time zone with the default location.

4. GregorianCalendar(int year, int month, int date, int hour, int minute, int second): It is a parameterized constructor of the GregorianCalendar class that constructs a GregorianCalendar with the given date and time in the default time zone with the default location.

5. GregorianCalendar(Locale location): It is a parameterized constructor of the GregorianCalendar class that constructs a GregorianCalendar based on the current time in the default time zone with the given location.

6. GregorianCalendar(TimeZone zone): It is a parameterized constructor of the GregorianCalendar class that constructs a GregorianCalendar based on the current time in the given time zone with the default location.

7. GregorianCalendar(TimeZone zone, Locale location): It is a parameterized constructor of the GregorianCalendar class that constructs a GregorianCalendar based on the current time in the given time zone with the given location.

GregorianCalendar Methods:

Code to understand the implementation of GregorianCalendar:

package com.DataFlair.DateAndTime;
import java.util.*;
public class GregoriancalendarImplementation
{
    public static void main(String args[]) {
      String Month[] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", 
         "October", "November", "December"};
      int year;
      GregorianCalendar calendar = new GregorianCalendar();
      System.out.print("Date: ");
      System.out.print(Month[calendar.get(Calendar.MONTH)]);
      System.out.print(" " + calendar.get(Calendar.DATE) + " ");
      System.out.println(year = calendar.get(Calendar.YEAR));
      System.out.print("Time: ");
      System.out.print(calendar.get(Calendar.HOUR) + ":");
      System.out.print(calendar.get(Calendar.MINUTE) + ":");
      System.out.println(calendar.get(Calendar.SECOND));
      if(calendar.isLeapYear(year)) {
         System.out.println("The current year is a leap year");
      }else {
         System.out.println("The current year is not a leap year");
      }
   }
}

The output of the above code:

Use of the Java Date & Time class

The Date and Time class in Java is mostly useful when the application works by tracking the time. E-commerce websites are used the most when it comes to providing sales over a particular period of time. Almost all the work of the industries is based on the scheduled task. Integrating the current date and time into the application results in tracking the changes at every point in time to benefit the business solution.

Conclusion

In this article, we saw how Java can be used to handle various operations using dates and times. This is a very important concept, as many software require proper handling of date and time to be implemented smoothly.