【Kotlin/Android Studio】現在の日付を取得する方法！DateTimeFormatterの使い方

val date = Date()
import java.time.LocalDate
import java.time.chrono.JapaneseDate
import java.time.LocalDateTime
import java.time.ZoneId
import java.time.ZonedDateTime

val date = Date()
val local = LocalDate.now()
val localTime = LocalDateTime.now()
val japan = JapaneseDate.now()
val zone = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"))
println(date)      // Sat Feb 17 00:41:41 UTC 2024
println(local)     // 2024-02-17
println(localTime) // 2024-02-17T00:41:41.172648120
println(japan)     // Japanese Reiwa 6-02-17
println(zone)      // 2024-02-17T09:41:41.193866743+09:00[Asia/Tokyo]

val now = LocalDateTime.now()
val df = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss")
val fdate = df.format(now)
print(fdate) // 2023/07/24 10:40:52

val now = LocalDateTime.now()
val df = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH時mm分ss秒")
val fdate = df.format(now)
print(fdate) // 2023年07月24日 11時04分39秒

val now = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"))
val df = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH時mm分ss秒")
val fdate = df.format(now)
print(fdate) // 2023年07月24日 20時07分32秒

val formatter = DateTimeFormatter.ofPattern("yyyy年M月d日")
val dateStr = "2023年10月23日"
val day = LocalDate.parse(dateStr, formatter)
print(day)        // 2023-10-23
print(day::class) // class java.time.LocalDate (Kotlin reflection is not available)

val formatter = DateTimeFormatter.ofPattern("yyyy年M月d日")
val dateStr = "2023年10月23日"
val day = formatter.parse(dateStr)
print(day)        // {},ISO resolved to 2023-10-23
print(day::class) // class java.time.format.Parsed (Kotlin reflection is not available)

val formatter = DateTimeFormatter.ofPattern("yyyy年M月d日 HH時mm分ss秒")
val dateStr = "2023年10月23日 10時20分30秒"
val day = LocalDateTime.parse(dateStr, formatter)
print(day)        // 2023-10-23T10:20:30

val japan = JapaneseDate.now()
val era = japan.era
print(era) // Reiwa
print(era.getDisplayName(TextStyle.FULL, Locale.JAPAN)) // 令和

val df = DateTimeFormatter.ofPattern("Gy年", Locale.JAPAN)
val jpEra = df.format(JapaneseDate.now())
print(jpEra)  // 令和5年

val date = "1999年12月1日"
val formatter = DateTimeFormatter.ofPattern("yyyy年M月d日", Locale.JAPAN)
val birthday = LocalDate.parse(date, formatter)
val japanDay = JapaneseDate.from(birthday)
val df = DateTimeFormatter.ofPattern("Gy年", Locale.JAPAN)
val jpEra = df.format(japanDay)
print(jpEra)  // 平成11年

val now = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"))
val oneDayBefore = now.minusDays(1)
val oneDayAfter = now.plusDays(1)
print(now)           // 2023-10-28T23:43:12.217434296+09:00[Asia/Tokyo]
print(oneDayBefore)  // 2023-10-27T23:43:12.217434296+09:00[Asia/Tokyo]
print(oneDayAfter)   // 2023-10-29T23:43:12.217434296+09:00[Asia/Tokyo]

val c = Calendar.getInstance()
val year = c.get(Calendar.YEAR)
val month = c.get(Calendar.MONTH)
val day = c.get(Calendar.DAY_OF_MONTH)   
val hour = c.get(Calendar.HOUR_OF_DAY)
val minute = c.get(Calendar.MINUTE)
val second = c.get(Calendar.SECOND)

print(year)         // 2023
print(month + 1 )   // 8
print(day)          // 3
print(hour)         // 12
print(minute)       // 32
print(second)       // 17

val date = Date()
val unixTimeMilliSeconds: Long = date.time // 1710855741810
val unixTimeSeconds: Long = unixTimeMilliSeconds / 1000 // 1710855741

var date = Date(unixTimeMilliSeconds)