How To Program In Java – Random Date – Birthday Example

This is how you would set up a Java class to generate a random birthday with a random month, day, and year.

This example will show how to use the Random class to generate each part of the date and handle different days for each month. It includes some advanced coding to include logic to determine if it is a leap year. I have included detailed comments explaining each part of the code.

// Import necessary classes
import java.util.Random;

public class RandomBirthday {

    // Attributes for birthday month, day, and year
    private int month;
    private int day;
    private int year;

    // Constructor - generates a random birthday when an object of RandomBirthday is created
    public RandomBirthday() {
        Random random = new Random(); // Create a new Random object

        // Generate a random year between 1900 and 2023
        year = random.nextInt(2023 - 1900 + 1) + 1900; // 1900 + 0 to 123

        // Generate a random month between 1 (January) and 12 (December)
        month = random.nextInt(12) + 1; // 1 to 12

        // Generate a day based on the month
        day = getRandomDayForMonth(month, random);
    }

    /**
     * Returns a random day based on the month. This accounts for different
     * numbers of days in each month and leap years for February.
     *
     * @param month  The month for which to generate a day (1 = January, 12 = December)
     * @param random The Random object to generate numbers
     * @return A valid day for the given month
     */
    private int getRandomDayForMonth(int month, Random random) {
        int day;

        // Determine the number of days in each month
        switch (month) {
            case 4: case 6: case 9: case 11: // Months with 30 days
                day = random.nextInt(30) + 1; // 1 to 30
                break;
            case 2: // February - could have 28 or 29 days
                if (isLeapYear(year)) {
                    day = random.nextInt(29) + 1; // 1 to 29 for leap years
                } else {
                    day = random.nextInt(28) + 1; // 1 to 28 for non-leap years
                }
                break;
            default: // Months with 31 days
                day = random.nextInt(31) + 1; // 1 to 31
                break;
        }

        return day;
    }

    /**
     * Determines if a given year is a leap year.
     *
     * @param year The year to check
     * @return true if the year is a leap year, false otherwise
     */
    private boolean isLeapYear(int year) {
        return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
    }

    /**
     * Returns the randomly generated birthday as a string in the format MM/DD/YYYY
     *
     * @return The birthday as a formatted string
     */
    public String getBirthday() {
        return String.format("%02d/%02d/%d", month, day, year); // Format as MM/DD/YYYY
    }

    // Main method to demonstrate functionality
    public static void main(String[] args) {
        // Create an instance of RandomBirthday
        RandomBirthday randomBirthday = new RandomBirthday();

        // Print the randomly generated birthday
        System.out.println("Random Birthday: " + randomBirthday.getBirthday());
    }
}

Explanation of the Code

1. Attributes (month, day, year):
   • These hold the month, day, and year for the randomly generated birthday.
2. Constructor:
   • The constructor initializes the year, month, and day attributes by generating random values using the Random object.
   • The year is set to a random number between 1900 and 2023.
   • The month is a random number between 1 and 12.
   • The day is determined based on the month and whether it’s a leap year (for February).
3. getRandomDayForMonth Method:
   • Uses a switch statement to determine the correct number of days in the given month.
   • February checks if the year is a leap year before setting the day.
4. isLeapYear Method:
   • A helper function that determines if a given year is a leap year using the standard leap year formula.
5. getBirthday Method:
   • Returns a formatted string representing the birthday in the format MM/DD/YYYY.
6. Main Method:
   • Creates an instance of RandomBirthday, which generates a new birthday.
   • Prints the generated birthday to the console.

Example Output

When you run this code, you might see output like:

Random Birthday: 03/15/1985

Or:

Random Birthday: 02/29/2000

Keywords and Key Facts

This Java code can help create a random date generator and how to apply the returned date to date formatting functions.