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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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