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abstract class Workout(val duration: Duration)
class Walking(duration: Duration) : Workout(duration)
class Swimming(duration: Duration) : Workout(duration)
class Running(duration: Duration) : Workout(duration)
// null object:
object NoWorkout : Workout(Duration.ZERO)
fun workoutService(date: LocalDate): Workout? {
val workouts = mapOf(
LocalDate.of(2020, 4, 25) to Walking(Duration.ofHours(2)),
LocalDate.of(2020, 4, 23) to Swimming(Duration.ofHours(1)),
LocalDate.of(2020, 4, 22) to Running(Duration.ofMinutes(30))
)
return workouts[date] ?: NoWorkout // usage of null object
}
fun main() {
val days = listOf(
LocalDate.of(2020, 4, 22), LocalDate.of(2020, 4, 23), LocalDate.of(2020, 4, 24), LocalDate.of(2020, 4, 25)
)
var sum: Long = 0
for(day in days) {
val workout = workoutService(day)
sum = sum + workout!!.duration.toMillis() // yes, we are that!! sure
}
println("Total duration: ${Duration.ofMillis(sum)}") // Total duration: PT3H30M
}
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