Careeroza

Real World Example

EMI Schedule and Delivery Estimate

Banking apps generate EMI due dates (same day every month, adjusted for short months), and e-commerce apps estimate delivery dates that skip Sundays. Both are simple with java.time.

Example

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;

public class Main {
    static final DateTimeFormatter F = DateTimeFormatter.ofPattern("EEE dd MMM yyyy");

    static LocalDate deliveryDate(LocalDate orderDate, int workingDays) {
        LocalDate d = orderDate;
        int added = 0;
        while (added < workingDays) {
            d = d.plusDays(1);
            if (d.getDayOfWeek() != DayOfWeek.SUNDAY) added++;
        }
        return d;
    }

    public static void main(String[] args) {
        LocalDate loanStart = LocalDate.of(2024, 1, 31);
        System.out.println("EMI schedule (due on the 31st or last day of month):");
        for (int i = 1; i <= 4; i++) {
            LocalDate due = loanStart.plusMonths(i);       // Feb 29, Mar 31, Apr 30...
            System.out.println("  EMI " + i + ": " + due.format(F));
        }

        LocalDate today = LocalDate.of(2024, 3, 25);
        LocalDate dueDate = LocalDate.of(2024, 3, 10);
        long overdue = ChronoUnit.DAYS.between(dueDate, today);
        System.out.println("Overdue by " + overdue + " days, late fee Rs " + overdue * 25);

        LocalDate ordered = LocalDate.of(2024, 3, 29);    // a Friday
        System.out.println("Ordered " + ordered.format(F) + ", arrives by " + deliveryDate(ordered, 3).format(F));
    }
}

Output

EMI schedule (due on the 31st or last day of month):
  EMI 1: Thu 29 Feb 2024
  EMI 2: Sun 31 Mar 2024
  EMI 3: Tue 30 Apr 2024
  EMI 4: Fri 31 May 2024
Overdue by 15 days, late fee Rs 375
Ordered Fri 29 Mar 2024, arrives by Tue 02 Apr 2024

Practice

Exercise: Write boolean isEligibleToVote(LocalDate dob, LocalDate onDate) that returns true when the person is at least 18 years old on that date.

Show answer
static boolean isEligibleToVote(LocalDate dob, LocalDate onDate) {
    return Period.between(dob, onDate).getYears() >= 18;
    // or: !dob.plusYears(18).isAfter(onDate)
}