STUDYECRAT Java : Date & Time API
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JavaDate & Time API
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★ Java 8 Date & Time API: Key Interview Points
1. Immutable Objects
LocalDate date = LocalDate.now();
LocalDate modifiedDate = date.plusDays(5);
// Original 'date' remains unchanged
LocalDate modifiedDate = date.plusDays(5);
// Original 'date' remains unchanged
- Tip: Always assign the result of date operations to new variables.
- Real Use: Thread-safe by design, eliminating synchronization issues.
2. DateTimeException Handling
try {
LocalDate invalidDate = LocalDate.of(2023, 2, 30);
} catch (DateTimeException e) {
System.out.println("Invalid date: " + e.getMessage());
}
// February 30 doesn't exist
LocalDate invalidDate = LocalDate.of(2023, 2, 30);
} catch (DateTimeException e) {
System.out.println("Invalid date: " + e.getMessage());
}
// February 30 doesn't exist
- Tip: Always validate user-input dates before processing.
- Real Use: Prevents crashes in calendar scheduling apps.
3. Period vs Duration
Period period = Period.between(
LocalDate.of(2023, 1, 1),
LocalDate.of(2023, 1, 31));
Duration duration = Duration.between(
LocalTime.of(10, 0), LocalTime.of(12, 30));
// Period for dates, Duration for time
LocalDate.of(2023, 1, 1),
LocalDate.of(2023, 1, 31));
Duration duration = Duration.between(
LocalTime.of(10, 0), LocalTime.of(12, 30));
// Period for dates, Duration for time
- Tip: Use Period for human-readable date differences (years/months/days).
- Real Use: Duration is perfect for calculating timeouts or session expirations.
4. TemporalAdjusters for Business Logic
LocalDate nextFriday = LocalDate.now()
.with(TemporalAdjusters.next(DayOfWeek.FRIDAY));
LocalDate quarterEnd = LocalDate.now()
.with(TemporalAdjusters.lastDayOfQuarter());
// Built-in business date calculations
.with(TemporalAdjusters.next(DayOfWeek.FRIDAY));
LocalDate quarterEnd = LocalDate.now()
.with(TemporalAdjusters.lastDayOfQuarter());
// Built-in business date calculations
- Tip: Create custom adjusters for company-specific fiscal calendars.
- Real Use: Automating payroll processing or financial reporting cycles.
5. ZoneId Daylight Saving Traps
ZonedDateTime dstStart = ZonedDateTime.of(
LocalDateTime.of(2023, 3, 12, 2, 30),
ZoneId.of("America/New_York"));
// March 12, 2023 2:30 AM doesn't exist in NY timezone
LocalDateTime.of(2023, 3, 12, 2, 30),
ZoneId.of("America/New_York"));
// March 12, 2023 2:30 AM doesn't exist in NY timezone
- Tip: Always use full timezone IDs (Region/City) instead of abbreviations.
- Real Use: Critical for global event scheduling applications.
💡 Pro Interview Tip
When asked about legacy Date classes vs Java 8 API, emphasize immutability, thread-safety, and ISO-8601 compliance as key advantages. Mention real-world pain points like Y2K38 problem (2038 Unix timestamp overflow) that the new API prevents.
