🧠 Super resumo mental
Duration → small units (hours/minutes)
Period → big units (years/months/days)
✅ Duration
Duration measures time in:
hours
minutes
seconds
It is used with:
LocalTime
LocalDateTime
👉 Think of Duration as clock-based time.
Example:
Duration.between(start, end);
It calculates how much time passed between two times.
✅ Period
Period measures time in:
years
months
days
It is used with:
LocalDate
👉 Think of Period as calendar-based time.
Example:
Period.between(startDate, endDate);
It calculates the difference in years, months, and days.
now(ZoneId) → quando quer hora de outro país
now(ZoneId) → when you want the time of another country
.now()
Gets the current date or time from the system.
.of()
Creates a date/time by passing numbers.
.parse()
Converts a String into a date/time object
✅ .now() → when you need the current moment
You use it when the system needs to know:
today’s date
the current time
the exact moment of a purchase
whether something is overdue
Real examples:
LocalDate today = LocalDate.now();
LocalDateTime purchaseMoment = LocalDateTime.now();
📌 Commonly used in:
payment systems
due date verification
logging systems
✅ .of() → when you already know the values
You use it when:
you are creating a fixed date
you are testing your code
you are defining a specific rule
LocalDate dueDate = LocalDate.of(2026, 5, 15);
📌 Commonly used in:
unit tests
system-defined dates
calculated or predefined dates
✅ .parse() → when the date comes as TEXT
You use it when:
you receive a date from the user
you receive a date from a database
you receive a date from an API
you read a date from a file
Example:
LocalDate date = LocalDate.parse("2026-05-15");
📌 Commonly used in:
forms
system integration
JSON data processing
✅ plusDays()
Adds days to a date.
LocalDate newDate = date.plusDays(10);
👉 Adds 10 days.
✅ plusWeeks()
Adds weeks to a date.
LocalDate newDate = date.plusWeeks(2);
👉 Adds 2 weeks (14 days).
✅ plusMonths()
Adds months to a date.
LocalDate newDate = date.plusMonths(3);
👉 Adds 3 months.
⚠ Important:
If the day does not exist in the new month, Java adjusts automatically.
Example:
LocalDate.of(2026, 1, 31).plusMonths(1);
Result → 2026-02-28
✅ plusYears()
Adds years to a date.
LocalDate newDate = date.plusYears(1);
👉 Adds 1 year.
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