JShell เป็น REPL (Read-Eval-Print-Loop) interactive tool ใน Java 9 รับ input ประเมินผลคืน output ให้ user
java.time.LocalDate class มีเมธอดมากมายสำหรับดึงข้อมูลวันที่: Day/Month/Year และ attributes ที่เกี่ยวข้อง Date meta-information: ข้อมูล classification เช่น leap year เป็นต้น LocalDate class เป็น immutable ใช้เมธอดต่างๆ add และ subtract days, months, years แต่ละเมธอดคืน instance ใหม่ของ LocalDate
Snippet 1: ดึงข้อมูลวันที่
jshell> import java.time.*;
jshell> LocalDate today = LocalDate.now()
today ==> 2020-04-22
jshell> today.getYear()
$3 ==> 2020
jshell> today.getDayOfWeek()
$4 ==> WEDNESDAY
jshell> today.getDayOfMonth()
$5 ==> 22
jshell> today.getDayOfYear()
$6 ==> 113
jshell> today.getMonth()
$7 ==> APRIL
jshell> today.getMonthValue()
$8 ==> 4
jshell> today.isLeapYear()
$9 ==> true
jshell> today.lengthOfYear()
$10 ==> 366
jshell> today.lengthOfMonth()
$11 ==> 30
Snippet 2: การบวก/ลบ วันที่
jshell> today.plusDays(50)
$12 ==> 2020-06-11
jshell> today.plusMonths(50)
$13 ==> 2024-06-22
jshell> today.plusYears(50)
$14 ==> 2070-04-22
jshell> today.minusYears(50)
$15 ==> 1970-04-22
jshell> LocalDate yesterYear = today.minusYears(50)
yesterYear ==> 1970-04-22
jshell> today
today ==> 2020-04-22 // ต้นฉบับไม่เปลี่ยน (immutable)
LocalDate Methods สำคัญ
| Category | Methods |
|---|---|
| Getting values | getYear(), getMonth(), getMonthValue(), getDayOfMonth(), getDayOfWeek(), getDayOfYear() |
| Checking | isLeapYear(), isBefore(), isAfter(), isEqual() |
| Length info | lengthOfMonth(), lengthOfYear() |
| Plus (add) | plusDays(), plusWeeks(), plusMonths(), plusYears(), plus(TemporalAmount) |
| Minus (subtract) | minusDays(), minusWeeks(), minusMonths(), minusYears(), minus(TemporalAmount) |
| With (modify) | withYear(), withMonth(), withDayOfMonth(), withDayOfYear(), with(TemporalAdjuster) |
| Static factories | now(), of(year, month, day), ofEpochDay(), parse(CharSequence) |
ตัวอย่างเพิ่มเติม
jshell> LocalDate christmas = LocalDate.of(2024, 12, 25)
christmas ==> 2024-12-25
jshell> christmas.getDayOfWeek()
$ ==> WEDNESDAY
jshell> LocalDate firstDayOfMonth = christmas.withDayOfMonth(1)
firstDayOfMonth ==> 2024-12-01
jshell> LocalDate nextFriday = christmas.with(java.time.temporal.TemporalAdjusters.next(java.time.DayOfWeek.FRIDAY))
nextFriday ==> 2024-12-27
jshell> Period period = Period.between(today, christmas)
period ==> P8M3D // 8 months 3 days
jshell> long daysUntil = today.until(christmas, java.time.temporal.ChronoUnit.DAYS)
daysUntil ==> 247
LocalDate vs LocalDateTime vs ZonedDateTime
| Class | Components | Use Case |
|---|---|---|
| LocalDate | Year, Month, Day | Birthday, anniversary, date-only |
| LocalTime | Hour, Minute, Second, Nano | Alarm time, opening hours |
| LocalDateTime | Date + Time (no zone) | Local appointments, logs |
| ZonedDateTime | Date + Time + Zone | Global events, timestamps |
| Instant | Epoch nanoseconds (UTC) | Machine timestamps, logging |
