Date & Time. Practical Tasks

The pattern MM/dd/YYYY looks harmless, yet for LocalDate.of(2024, 12, 30) it prints 12/30/2025: the capital Y is the week-based year, not the calendar year. The program passes every test you run in March and ships a wrong year in the last days of December — a bug that is much cheaper to catch in a practice problem than in a report a customer has already received.

These Java date and time exercises practise the java.time API added in Java 8: LocalDate, LocalTime, LocalDateTime, Instant, Period, Duration and formatting with DateTimeFormatter. The page has 7 LocalDate and java.time practice problems with hints — from printing facts about your date of birth to two parts of the course practice projects: the employee salary report and the online store receipt. The theory is in the lesson Java Date and Time API: java.time and the Current Date and the lessons of the module that follow it.

LocalDate Methods: Your Date of Birth

1. Create a LocalDate object with your date of birth using LocalDate.of(year, month, day).
2. Print the day of the week, the day of the year, the month and the year of this date.
3. Create a LocalDate object with the current date.
4. Compare the current date with your date of birth using isAfter(), isBefore() and isEqual(), and print the results.

Example output for the date of birth March 15, 2000:

Day of week: WEDNESDAY
Day of year: 75
Month: MARCH
Year: 2000
Today is after the birthday: true

Holiday Calendar for the Current Year

1. Get the current year with Year.now() or LocalDate.now().getYear().
2. Make a list of 5–7 holidays with a fixed date (for example, New Year’s Day, Valentine’s Day, Independence Day, Halloween, Christmas Day, or the holidays of your country): a Map<LocalDate, String> or a list of «date + name» objects.
3. Print the holiday schedule in date order with DateTimeFormatter: the day of the week, the month name and the day — in English, whatever the default locale of the JVM is.

Example output line for 2026:

Saturday, July 4 — Independence Day

Age and Days Until the Next Birthday

1. Store a date of birth as a LocalDate.
2. Use Period.between() to print the exact age: full years, months and days.
3. Count the days left until the next birthday. If this year’s birthday has already passed, count to the birthday next year; if it is today, print a greeting instead.
4. Test the program with a birthday on February 29 (for example, 02/29/2004).

Example output for the date of birth 03/15/2000 if today is 10/20/2026:

Age: 26 years 7 months 5 days
Days until the birthday: 146

Work Shift Duration with LocalTime and Duration

1. Define several shifts as pairs of LocalTime values «start — end», including at least one night shift: 09:00–18:00, 08:30–17:15, 22:00–06:00.
2. For each shift, print its length in hours and minutes using Duration.
3. Print the total length of all shifts.

Expected output:

09:00–18:00: 9 h 0 min
08:30–17:15: 8 h 45 min
22:00–06:00: 8 h 0 min
Total: 25 h 45 min

Measure Code Execution Time with Instant

1. Before the work starts, save the moment Instant.now() and print the start time in the format HH:mm:ss.
2. Build a string of the numbers from 1 to 20,000 in two ways: with += concatenation in a loop and with a StringBuilder.
3. For each way, print the execution time in milliseconds with Duration.between(start, end).toMillis().

The exact numbers depend on the computer, but the difference between the two ways will be clear. Output format:

Start: 14:05:31
Concatenation +=: ... ms
StringBuilder: ... ms

Salary Date in the Employee Report

Employee Report · part 2 of 3 · ← part 2

1. Add a field LocalDate salaryDate (the payday) to the Employee class from part 1 of the project.
2. Create a FullReport class that prints the same information as Report and adds a column with the salary date in the format MM/dd/yyyy.

Example output (the column widths are up to you):

John Smith             4500.00  10/30/2026
Mary Johnson           5200.50  10/30/2026

Date and Time on the Purchase Receipt

Online Store · part 5 of 5 · ← part 4

Add the date and time of the order to the purchase receipt from the previous part:

Date: 03/28/2019 21:10:58

Product        Price
--------------------
Jeans      $1,500.78
Skirt      $1,000.56
Tie          $500.78
--------------------
Total:     $3,002.12

Solution on Patreon →

What to Review Before You Start

All seven exercises need only seven classes from the java.time package. The table shows what each class stores, where it is explained and which exercises use it. Every one of these classes is immutable: plusDays(), withYear() and similar methods return a new object and leave the original unchanged.

Date and Time Bugs That Compile Fine

Most wrong solutions to java.time exercises come from a wrong letter in a formatting pattern, a lost result of plusDays() and confusing Period with Duration. Such code compiles and often works, but prints a wrong date or throws an exception only on certain data.

What does this code print?

LocalDate date = LocalDate.of(2024, 12, 30);
System.out.println(date.format(DateTimeFormatter.ofPattern("MM/dd/YYYY", Locale.US)));
System.out.println(date.format(DateTimeFormatter.ofPattern("MM/dd/yyyy")));
// Output:
// 12/30/2025
// 12/30/2024

December 30, 2024 is a Monday, and the week it belongs to already counts as week 1 of 2025 under both the US and the ISO-8601 week rules, so the pattern with YYYY prints the «next» year. The bug appears only in the last days of December and the first days of January, which is why it slips through review. The meaning of every letter is in DateTimeFormatter pattern letters. Other frequent slips: