In Java, the Calendar class is used to work with dates and times. It is an abstract class which offers conversion method between a Date object and to many integer attributes, including year, month, day, hour, minute, second, and millisecond.
Adding or subtracting days, months, or years is only one of the many operations that the Calendar class offers methods for doing on dates and times.
In Java, a String is an object that represents a sequence of characters. It is a fundamental data type and is used extensively in Java programs for storing and manipulating textual data.
What are the reasons for converting calendar to string in Java
There are several reasons why you might want to convert a Calendar object to a String in Java:
- Displaying the date and time: Date and time are made readable and recognisable for consumers by converting Calendar to String, which also improves programme usability.
- Storing the date and time: Storing date and time may require converting to String. Standardized formats like ISO 8601 or RFC 3339 ensure easy parsing by other programs.
- Transmitting the date and time: Transmitting date and time over a network may require converting it to a String. Standardized formats ensure easy parsing by other programs.
- Comparing dates and times: To compare two Calendar objects, you can convert them to String objects using a standardized format.
Methods for converting Calendar to String in Java:
Here are some commonly used methods for converting a Calendar object to a String in Java:
- Using SimpleDateFormat:
- Using DateTimeFormatter (Java 8 and later):
- Using String.format():
- Using java.text.DateFormat:
- Using java.time.format.DateTimeFormatter (Java 8 and later):
Approach 1: Using SimpleDateFormat
Java SimpleDateFormat and DateFormat classes are used for date formatting. It is mostly used where we need to display or utilize the date and time functionality of Java. Both of these classes are present in the com.text package.
Code:
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Scanner;
public class CalendarToStringExample {
public static void main(String[] args) {
// Prompt the user to enter a date and time
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the date and time (yyyy-MM-dd HH:mm:ss): ");
String input = scanner.nextLine();
// Parse the user input into a Calendar object
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Calendar calendar = Calendar.getInstance();
try {
calendar.setTime(dateFormat.parse(input));
} catch (Exception e) {
System.out.println("Invalid input: " + input);
return;
}
// Convert the Calendar object to a String
String dateString = dateFormat.format(calendar.getTime());
// Print the result
System.out.println("The date and time in string format is: " + dateString);
}
}
Output:
Enter the date and time (yyyy-MM-dd HH:mm:ss): 2023-04-23 14:30:00
The date and time in string format is: 2023-04-23 14:30:00
Explanation:
- The user input is parsed into a Calendar object using a SimpleDateFormat object, enabling manipulation and time and date calculation.
- The programme generates an error message and terminates if the user input is invalid or cannot be interpreted.
- The Calendar object is then converted back into a string format using the same SimpleDateFormat object.
- Finally, the program outputs the resulting string to the console.
Approach 2: Using DateTimeFormatter (Java 8 and later)
The DateTimeFormatter class provides mainly one method to format a given date-time instance of any type. It formats the dateTimeObject instance using the specified format.
String formmatedString = dateTimeObject.format(formatter);
Code:
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Calendar;
import java.util.Scanner;
public class CalendarToStringExample {
public static void main(String[] args) {
// Prompt the user to enter a date and time
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the date and time (yyyy-MM-dd HH:mm:ss): ");
String input = scanner.nextLine();
// Parse the user input into a Calendar object
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime dateTime = LocalDateTime.parse(input, formatter);
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(dateTime.atZone(java.time.ZoneId.systemDefault()).toInstant().toEpochMilli());
// Convert the Calendar object to a String
String dateString = formatter.format(dateTime);
// Print the result
System.out.println("The date and time in string format is: " + dateString);
}
}
Output:
Enter the date and time (yyyy-MM-dd HH:mm:ss): 2023-04-23 14:30:00
The date and time in string format is: 2023-04-23 14:30:00
Explanation:
- It uses the Scanner class to read the user input as a String.
- It then creates a DateTimeFormatter object to parse the String input into a LocalDateTime object.
- The LocalDateTime object is then used to set the time in a Calendar object, which can be useful for performing date and time operations.
- The programme then uses the DateTimeFormatter object to format the date and time as a String and prints it to the terminal.
Approach 3: Using String.format()
The java string format() method returns the formatted string by given locale, format and arguments. If you don’t specify the locale in the String.format() method, it uses the default locale by calling Locale.getDefault() method.
Code:
import java.util.Calendar;
import java.util.Scanner;
public class CalendarToStringExample {
public static void main(String[] args) {
// Prompt the user to enter a date and time
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the date and time (yyyy-MM-dd HH:mm:ss): ");
String input = scanner.nextLine();
// Parse the user input into a Calendar object
Calendar calendar = Calendar.getInstance();
try {
String[] dateTime = input.split(" ");
String[] dateParts = dateTime[0].split("-");
String[] timeParts = dateTime[1].split(":");
int year = Integer.parseInt(dateParts[0]);
int month = Integer.parseInt(dateParts[1]) - 1; // months are 0-based in Calendar
int day = Integer.parseInt(dateParts[2]);
int hour = Integer.parseInt(timeParts[0]);
int minute = Integer.parseInt(timeParts[1]);
int second = Integer.parseInt(timeParts[2]);
calendar.set(year, month, day, hour, minute, second);
} catch (Exception e) {
System.out.println("Invalid input: " + input);
return;
}
// Convert the Calendar object to a String
String dateString = String.format("%1$tY-%1$tm-%1$td %1$tH:%1$tM:%1$tS", calendar);
// Print the result
System.out.println("The date and time in string format is: " + dateString);
}
}
Output:
Enter the date and time (yyyy-MM-dd HH:mm:ss): 2023-04-23 14:30:00
The date and time in string format is: 2023-04-23 14:30:00
Explanation:
- It parses the user input and converts it to a Calendar object.
- The calendar is used by the programme.The year, month, day, hour, minute, and second fields of a Calendar object are set based on user input once it is obtained using the getInstance() function and represents the current date and time.
- The Calendar object is converted into a String using the String.format() method with the specific format string “%1$tY-%1$tm-%1$td%1$tH:%1$tM:%1$tS” as the required output format.
- The resulting String is printed to the console.
Approach 4: Using java.text.DateFormat
The java.text.DateFormat class provides various methods to format and parse date and time in java in language-independent manner. The DateFormat class is an abstract class. java.text. The Format is the parent class and java.text.SimpleDateFormat is the subclass of java.text.DateFormat class.
Code:
import java.util.Calendar;
import java.util.Scanner;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
public class CalendarToStringExample {
public static void main(String[] args) {
// Prompt the user to enter a date and time
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the date and time (yyyy-MM-dd HH:mm:ss): ");
String input = scanner.nextLine();
// Parse the user input into a Calendar object
Calendar calendar = Calendar.getInstance();
try {
String[] dateTime = input.split(" ");
String[] dateParts = dateTime[0].split("-");
String[] timeParts = dateTime[1].split(":");
int year = Integer.parseInt(dateParts[0]);
int month = Integer.parseInt(dateParts[1]) - 1; // months are 0-based in Calendar
int day = Integer.parseInt(dateParts[2]);
int hour = Integer.parseInt(timeParts[0]);
int minute = Integer.parseInt(timeParts[1]);
int second = Integer.parseInt(timeParts[2]);
calendar.set(year, month, day, hour, minute, second);
} catch (Exception e) {
System.out.println("Invalid input: " + input);
return;
}
// Convert the Calendar object to a String
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = dateFormat.format(calendar.getTime());
// Print the result
System.out.println("The date and time in string format is: " + dateString);
}
}
Output:
Enter the date and time (yyyy-MM-dd HH:mm:ss): 2023-04-23 14:30:00
The date and time in string format is: 2023-04-23 14:30:00
Explanation:
- Program reads the user input using a Scanner object and stores it in a string variable called input.
- The getInstance() function of the Calendar class is used to generate a calendar object.
- The user input is then parsed into a Calendar object using the split() method to separate the date and time values.
- The year, month, day, hour, minute, and second values derived from user input are set using the Calendar object’s set() method.
- The SimpleDateFormat class is used to format the Calendar object into a string in the same format as the user input.
- The formatted date string is printed to the console using System.out.println().
Approach 5: Using java.time.format.DateTimeFormatter
DateTimeFormatterBuilder Class is a builder class that is used to create date-time formatters. It allows a DateTimeFormatter to be created. It is used for constructing formatters which are then used to print or parse. The formatters are built by appending specific fields or other formatters to an instance of this builder.
Code:
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Scanner;
public class CalendarToStringExample {
public static void main(String[] args) {
// Prompt the user to enter a date and time
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the date and time (yyyy-MM-dd HH:mm:ss): ");
String input = scanner.nextLine();
// Parse the user input into a LocalDateTime object
LocalDateTime dateTime = null;
try {
dateTime = LocalDateTime.parse(input, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
} catch (Exception e) {
System.out.println("Invalid input: " + input);
return;
}
// Convert the LocalDateTime object to a String
String dateString = dateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
// Print the result
System.out.println("The date and time in string format is: " + dateString);
}
}
Output:
Enter the date and time (yyyy-MM-dd HH:mm:ss): 2023-04-23 14:30:00
The date and time in string format is: 2023-04-23 14:30:00
Explanation:
- Parse the user input into a LocalDateTime object
- Convert the LocalDateTime object to a String using the format method of the DateTimeFormatter class
- Display the resulting date and time in string format.
The programme will terminate and display an error notice if the input is incorrect.
Best Approach for converting calendar to string in Java
Following are the some reasons to make Java’s built-in SimpleDateFormat class a best method
- A straightforward and adaptable method for formatting and parsing dates and times is provided by Java’s built-in SimpleDateFormat class.
- It enables you to enter a pattern that specifies the output string’s format, including the placement and kind of date and time elements.
- Because SimpleDateFormat is thread-safe, multi-threaded programmes can utilize it without fear of synchronization problems.
- Because of the API’s popularity and thorough documentation, finding examples and solving problems is simple.
Sample Problem for converting calendar to string in Java
Sample problem 1
Suppose you are working on a project for a car rental company. The company allows customers to make reservations for rental cars online, and the system needs to generate confirmation emails to send to customers once their reservations are confirmed.
To generate the confirmation email, you need to convert the pickup date and time and the return date and time to strings in a specific format. You could use SimpleDateFormat to do this.
Solution:
- Prompt the user to enter the pickup and return dates in the format “yyyy-MM-dd HH:mm”.
- Parse the user input strings into Calendar objects using a SimpleDateFormat object.
- Convert the Calendar objects to strings in the format “EEEE, MMMM d, yyyy ‘at’ h:mm a” using another SimpleDateFormat object.
- Generate the confirmation email text using the formatted pickup and return date strings.
- Print the confirmation email text to the console.
Code:
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Scanner;
public class CarRentalConfirmationEmail {
public static void main(String[] args) {
// Prompt the user to enter the reservation details
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the pickup date and time (yyyy-MM-dd HH:mm): ");
String pickupDateString = scanner.nextLine();
System.out.print("Enter the return date and time (yyyy-MM-dd HH:mm): ");
String returnDateString = scanner.nextLine();
// Parse the user input into Calendar objects
Calendar pickupDate = Calendar.getInstance();
Calendar returnDate = Calendar.getInstance();
try {
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm");
pickupDate.setTime(dateFormat.parse(pickupDateString));
returnDate.setTime(dateFormat.parse(returnDateString));
} catch (Exception e) {
System.out.println("Invalid input. Please enter the dates in the format yyyy-MM-dd HH:mm");
return;
}
// Convert the Calendar objects to strings in the required format
SimpleDateFormat outputDateFormat = new SimpleDateFormat("EEEE, MMMM d, yyyy 'at' h:mm a");
String pickupDateStringFormatted = outputDateFormat.format(pickupDate.getTime());
String returnDateStringFormatted = outputDateFormat.format(returnDate.getTime());
// Generate the confirmation email and print it
String emailText = "Dear customer,\n\nYour reservation has been confirmed. You have reserved a car from " +
pickupDateStringFormatted + " to " + returnDateStringFormatted + ".\n\nThank you for choosing our company!";
System.out.println(emailText);
}
}
Output:
Enter the pickup date and time (yyyy-MM-dd HH:mm): 2023-05-01 10:30
Enter the return date and time (yyyy-MM-dd HH:mm): 2023-05-03 15:45
Dear customer,
Your reservation has been confirmed. You have reserved a car from Tuesday, May 2, 2023 at 10:30 AM to Thursday, May 4, 2023 at 3:45 PM.
Thank you for choosing our company!
Note: When an exception is thrown while the input strings are being parsed, the programme manages it by capturing it and outputting an error message to the terminal.
Sample problem 2
A company has a shift schedule where employees work in shifts that start and end at specific times. The company wants to generate a report that lists the start and end times of each shift in a user-friendly format.
Solution using DateTimeFormatter:
Input (user-defined):
- An ArrayList of Calendar objects representing the start times of each shift
- An integer value representing the shift duration in hours
Explanation:
- The current date and time is added as the first shift start time using the Calendar.getInstance() method.
- By parsing a string representation of a date and time into a Calendar object, the getCalendar() function adds two more shift start timings to the ArrayList.
- The duration of each shift is set to 8 hours.
- A DateTimeFormatter is created to format the output of the shift start and end times.
- The program loops through the ArrayList of shift start times, calculates the corresponding shift end time by adding the shift duration, and formats the start and end times using the DateTimeFormatter.
- The formatted start and end times for each shift are printed to the console.
Code:
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.Calendar;
public class Main {
public static void main(String[] args) {
ArrayList<Calendar> shiftStartTimes = new ArrayList<Calendar>();
shiftStartTimes.add(Calendar.getInstance()); // Add the current date and time as the first shift start time
shiftStartTimes.add(getCalendar("2023-04-25T17:00:00"));
shiftStartTimes.add(getCalendar("2023-04-26T01:00:00"));
int shiftDuration = 8;
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm a");
System.out.println("Shift Report");
System.out.println("------------");
for (int i = 0; i < shiftStartTimes.size(); i++) {
Calendar shiftStart = shiftStartTimes.get(i);
Calendar shiftEnd = (Calendar) shiftStart.clone();
shiftEnd.add(Calendar.HOUR_OF_DAY, shiftDuration);
String formattedStartTime = formatter.format(shiftStart.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime());
String formattedEndTime = formatter.format(shiftEnd.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime());
System.out.println("Shift " + (i+1) + " - Start Time: " + formattedStartTime + ", End Time: " + formattedEndTime);
}
}
public static Calendar getCalendar(String dateString) {
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
Calendar calendar = Calendar.getInstance();
try {
calendar.setTime(dateFormat.parse(dateString));
} catch (ParseException e) {
e.printStackTrace();
}
return calendar;
}
}
Output:
Shift Report
------------
Shift 1 - Start Time: 2023-04-26 02:56 PM, End Time: 2023-04-26 10:56 PM
Shift 2 - Start Time: 2023-04-25 05:00 PM, End Time: 2023-04-26 01:00 AM
Shift 3 - Start Time: 2023-04-26 01:00 AM, End Time: 2023-04-26 09:00 AM
Sample problem 3
Suppose you are building a scheduling application that needs to display the date and time of appointments in a specific format. You want to display the date and time in the format “MM/DD/YYYY HH:MM AM/PM” (e.g. “04/25/2023 02:30 PM”) for all appointments. To do this, use String.format() to transform the Calendar object that represents each appointment’s time and date into a String.
Solution:
- The code takes a user-defined date and time as a Calendar object.
- The String.format() method is then applied to the date and time to format it as a string.
- The format string %1$tm/%1$td/%1$tY %1$tI:%1$tM %1$Tp is used to specify the desired date and time format.
- The formatted date and time string is stored in the formattedDate variable.
- The formatted date, as well as time string, is then output to the console using System.out.println().
Code:
import java.util.Calendar;
public class CalendarToStringExample {
public static void main(String[] args) {
// User defined input
Calendar appointmentDate = Calendar.getInstance();
appointmentDate.set(2023, 3, 25, 14, 30); // Year, month, day, hour, minute
// Convert Calendar to String using String.format()
String formattedDate = String.format("%1$tm/%1$td/%1$tY %1$tI:%1$tM %1$Tp", appointmentDate);
// Output the result
System.out.println("Appointment date and time: " + formattedDate);
}
}
Output:
Appointment date and time: 04/25/2023 02:30 PMSample problem 4
An appointment scheduling system needs to display the appointment time and date in a human-readable format for the user. The appointment date and time information is stored as a Calendar object, and the system needs to convert it to a string using java.text.DateFormat class.
Solution:
This program generates an appointment time in the format of “EEEE, MMMM dd, yyyy ‘at’ h:mm a” using the Calendar and DateFormat classes in Java.
Here are the steps of the program:
- Get the current date and time using Calendar.getInstance() method.
- Define the date format using SimpleDateFormat class.
- Convert the appointment time to a string using the format() method of the SimpleDateFormat class.
- Display the appointment time string using System.out.println() method.
import java.util.Calendar;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
public class AppointmentSystem {
public static void main(String[] args) {
// Get the appointment time
Calendar appointmentTime = Calendar.getInstance();
// Define the date format
DateFormat dateFormat = new SimpleDateFormat("EEEE, MMMM dd, yyyy 'at' h:mm a");
// Convert the appointment time to a string
String appointmentTimeString = dateFormat.format(appointmentTime.getTime());
// Display the appointment time string
System.out.println("Your appointment is scheduled for: " + appointmentTimeString);
}
}
Output:
Your appointment is scheduled for: Saturday, April 23, 2023 at 2:00 PMSample Problem 5:
The departure and arrival timings of a flight must be shown to the user via a flight booking system in a human-readable format. The departure and arrival times are stored as java.util.Calendar objects, and the system needs to convert them to strings using java.time.format.DateTimeFormatter class (Java 8 and later).
Solution:
- Get the departure and arrival times as Calendar objects.
- Convert the departure and arrival times to LocalDateTime objects.
- Define a DateTimeFormatter to format the date-time strings.
- Convert the departure and arrival times to formatted strings using the DateTimeFormatter.
- Print the formatted departure and arrival time strings to the console.
Code:
import java.util.Calendar;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
public class FlightBookingSystem {
public static void main(String[] args) {
// Get the departure and arrival times
Calendar departureTime = Calendar.getInstance();
departureTime.set(2023, 4, 23, 10, 30, 0);
Calendar arrivalTime = Calendar.getInstance();
arrivalTime.set(2023, 4, 23, 15, 15, 0);
// Convert the departure and arrival times to LocalDateTime objects
LocalDateTime departureDateTime = LocalDateTime.ofInstant(departureTime.toInstant(), ZoneId.systemDefault());
LocalDateTime arrivalDateTime = LocalDateTime.ofInstant(arrivalTime.toInstant(), ZoneId.systemDefault());
// Define the date-time formatter
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("E, d MMM yyyy h:mm a");
// Convert the departure and arrival times to formatted strings
String departureTimeString = departureDateTime.format(dateTimeFormatter);
String arrivalTimeString = arrivalDateTime.format(dateTimeFormatter);
// Display the departure and arrival time strings
System.out.println("Flight departure time: " + departureTimeString);
System.out.println("Flight arrival time: " + arrivalTimeString);
}
}
Output:
Flight departure time: Tue, 23 May 2023 10:30 AM
Flight arrival time: Tue, 23 May 2023 3:15 PM
Conclusion:
In this blog, we discussed several methods for converting a calendar to a string in Java. For each method, we provided sample code with user-defined input and output. We also discussed the importance of converting a calendar to a string in Java.
Overall, the conversion of a calendar to a string in Java is a common operation in various applications. It allows for easier manipulation and presentation of dates and times in various formats that are more human-readable.
24×7 Live Java Homework Help From Expert Tutors!
