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Java Age Calculator Program (from Date/Year of Birth)

In a world driven by technology and innovation, programming is an invaluable skill that opens up several new possibilities. Java, as one of the most popular and versatile programming languages, provides a solid foundation for developing a wide range of applications. 

In this tutorial, we will create a practical and useful program for Age Calculator in Java.

The Age Calculator program in Java is a simple yet effective tool that allows users to find their age or the age of others by date of birth. Whether you're a budding programmer looking to expand your skills or someone with a curiosity for how software applications work, this tutorial will guide you through the process step by step.

Concepts Used:

Age Calculator in Java Using Class

Here's an example of an age calculator program in Java using the Date and Calendar classes:

Code

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

public class AgeCalculator {

    public static void main(String[] args) {
        // Get the current date
        Calendar currentDate = Calendar.getInstance();
        Date now = currentDate.getTime();

        // Set the birthdate
        Calendar birthDate = Calendar.getInstance();
        birthDate.set(1990, Calendar.JANUARY, 1); // Replace with the birthdate you want to calculate from

        // Calculate the age
        int age = currentDate.get(Calendar.YEAR) - birthDate.get(Calendar.YEAR);

        // Check if the birthday hasn't occurred yet this year
        if (currentDate.get(Calendar.MONTH) < birthDate.get(Calendar.MONTH) || 
           (currentDate.get(Calendar.MONTH) == birthDate.get(Calendar.MONTH) &&
           currentDate.get(Calendar.DAY_OF_MONTH) < birthDate.get(Calendar.DAY_OF_MONTH))) {
            age--;
        }

        // Format and display the result
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        String birthDateString = dateFormat.format(birthDate.getTime());
        String currentDateString = dateFormat.format(now);

        System.out.println("Date of Birth: " + birthDateString);
        System.out.println("Current Date: " + currentDateString);
        System.out.println("Age: " + age + " years");
    }
}

Output

Date of Birth: 1990-01-01
Current Date: 2023-09-28
Age: 33 years

Explanation

This program first obtains the current date and time using Calendar.getInstance() and getTime().

It sets a date of birth (you can replace it with the birthdate you want to calculate from) using another Calendar instance.

It calculates the age by subtracting the birth year from the current year.

It then checks if the birthday for the current year has already occurred. If not, it subtracts one from the calculated age.

Finally, it formats and displays the birthdate, current date, and age in years.

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Java Age Calculator Using java.time

Here's an age calculator program in Java using the java.time package introduced in Java 8:

Code

import java.time.LocalDate;
import java.time.Period;
import java.time.format.DateTimeFormatter;

public class AgeCalculator {

    public static void main(String[] args) {
        // Define the birthdate
        LocalDate birthDate = LocalDate.of(1990, 1, 1); // Replace with the birthdate you want to calculate from

        // Get the current date
        LocalDate currentDate = LocalDate.now();

        // Calculate the age
        Period age = Period.between(birthDate, currentDate);

        // Format and display the result
        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        String birthDateString = birthDate.format(dateFormatter);
        String currentDateString = currentDate.format(dateFormatter);

        System.out.println("Birthdate: " + birthDateString);
        System.out.println("Current Date: " + currentDateString);
        System.out.println("Age: " + age.getYears() + " years, " + age.getMonths() + " months, " + age.getDays() + " days");
    }
}

Output

Birthdate: 1990-01-01
Current Date: 2023-09-28
Age: 33 years, 8 months, 27 days

Explanation

  • This program uses the java.time.LocalDate class to work with dates.

  • It defines the birthdate using LocalDate.of().

  • The current date is obtained using LocalDate.now().

  • The age is calculated using Period.between().

Calculate Age in Java Using External Library

Here's an age calculator program in Java using external libraries like Joda-Time (although it's deprecated in favor of the java.time package):

Please note that you may need to include the Joda-Time library in your project to use this method.

Code

import org.joda.time.DateTime;
import org.joda.time.Years;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

public class AgeCalculator {

    public static void main(String[] args) {
        // Define the birthdate
        String birthDateString = "1990-01-01"; // Replace with the birthdate you want to calculate from
        DateTimeFormatter dateFormatter = DateTimeFormat.forPattern("yyyy-MM-dd");
        DateTime birthDate = DateTime.parse(birthDateString, dateFormatter);

        // Get the current date
        DateTime currentDate = DateTime.now();

        // Calculate the age
        Years age = Years.yearsBetween(birthDate, currentDate);

        // Format and display the result
        System.out.println("Birthdate: " + birthDateString);
        System.out.println("Current Date: " + currentDate.toString(dateFormatter));
        System.out.println("Age: " + age.getYears() + " years");
    }
}

Output

Birthdate: 1990-01-01
Current Date: 2023-09-28
Age: 33 years

Explanation

This program uses the Joda-Time library for date and time calculations.

  • It defines the birthdate as a string and parses it into a DateTime object using a specified date format.

  • The current date is obtained using DateTime.now().

  • The age is calculated using Years.yearsBetween().

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