Programming study diary

October 29, 2020 Since I dealt with the Calendar class in Java, I will briefly summarize how to use it.

What is the Calendar class?

A class for manipulating dates and specified dates and times. Used to calculate, get, and set the date and time in Java.

In the Calendar class, create an object by calling the getInstance method instead of the operator new. The getInstance method returns an object initialized to the current date and time each time it is called. When using it, be sure to specify ʻimport java.util.Calendar`.

Sample code

import java.util.Calendar

public class Main {
  public static void main(String[] args) throws Exception {
    Calendar calendar = Calendar.getInstance();
    System.out.println(calendar.get(Calendar.YEAR) + "Year" + calendar.get(Calendar.MONTH)+ "Moon" + calendar.get(Calendar.DATE) + "Day" );
  }
}

`Execution result`


October 29, 2020

How to use basic methods

set method

The set method is used to set the date and time. Therefore, it is often used in programs that process dates.

Note that in the example below, the previous values will remain except for the specified element (years in this case).

`How to use`


import java.util.Calendar

public class Main {
  public static void main(String[] args) throws Exception {
    Calendar calendar = Calendar.getInstance();
    System.out.println("Current date and time:" + calendar.getTime().toString());

    //Set the year to 2022
    calendar.set(Calendar.YEAR, 2022);
    System.out.println("Set 2022 for the year:" + calendar.getTime());
  }
}

`Execution result`


Current date and time: Thu Oct 29 10:43:58 UTC 2020
Set the year to 2022: Thu Oct 29 10:43:58 UTC 2022

add method

Use the add method when adding or subtracting dates in the Calendar class.

`How to use`


import java.util.Calendar

public class Main {
  public static void main(String[] args) throws Exception {
    Calendar calendar = Calendar.getInstance();
    System.out.println("Current date and time:" + calendar.getTime().toString());

    //Add 1 year
    calendar.add(Calendar.YEAR, 1);
    System.out.println("Increase by one year:" + calendae.getTime());
  }
}

`Execution result`


Current date and time: Thu Oct 29 10:43:58 UTC 2020
Increase by 1 year: Thu Oct 29 10:43:58 UTC 2021

format method

You can specify the date format with a character string.

import java.text.SimpleDateFormat;
import java.util.Calendar;
 
public class Main {
  public static void main(String[] args) {
     Calendar calendar = Calendar.getInstance();

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy year MM month dd day");
    System.out.println(sdf.format(calendar.getTime())); 
  }
}

`Execution result`


October 20, 2020

References

[Java] How to use the Calendar class that can be used to calculate and get the date and time! [Introduction to Java] Complete explanation of how to use the Calendar class (set / add / format) [Introduction to Java] Specify the date format of Calendar (format) [Introduction to Java] How to use Calendar (add)