class Car(val id: String) {
var speed: Double = 0.0
}
public class Car() {
public final String id;
public Double speed;
public Car(String id) {
this.id = id;
this.speed = 0.0;
}
}
* DTO /
** / ,
Kotlin NPE. id, speed Kotlin null.
var car: Car = Car(null) // compile error
car.speed = null // compile error
, .
fun toRoman(value: Int): String {
val singles = arrayOf("", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX")
val tens = arrayOf("", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC")
val hundreds = arrayOf("", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM")
val thousands = arrayOf("", "M", "MM", "MMM")
val roman = thousands[value / 1000] + hundreds[value % 1000 / 100] + tens[value % 100 / 10] + singles[value % 10]
return roman
}
public String toRoman(int value) {
final String[] singles = new String[] { "", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX" };
final String[] tens = new String[] { "", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC" };
final String[] hundreds = new String[] { "", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM" };
final String[] thousands = new String[] { "", "M", "MM", "MMM" };
final String roman = thousands[value / 1000] + hundreds[value % 1000 / 100] + tens[value % 100 / 10] + singles[value % 10];
return roman;
}
, ? final . , final Java . .
:
val data:List = ArrayList()
val sum = data.filter { it > 0 }.sum()
List data = new ArrayList<>();
final Integer[] sum = { 0 }; //Variable used in lambda expression should be final or effectively final
data.stream().filter(value -> value > 0).forEach(value -> sum[0] += value);
. Kotlin jvm 6, Java jvm 8 . , 24 API. 5 9,5% . final or effectively final Java.
interface Property {
var value: T
val rx: Observable
}
open class BaseProperty(defaultValue: T) : Property {
override var value: T = defaultValue
set(value) {
field = value
_rx.onNext(field)
}
private val _rx = PublishSubject.create()
override val rx: Observable = _rx
get() {
return field.startWith(value)
}
}
val rx. Observable . .. json'a . startWith .
class Car {
private val _speed = BaseProperty(0.0)
var speed: Double
get() = _speed.value
set(value) {
_speed.value = value
}
@JsonIgnore
val rxSpeed: Observable = _speed.rx
}
class Police {
val cars: List = listOf(Car("1st"), Car("2nd"), Car("3rd"))
init {
cars.forEach {
car -> car.rxSpeed
.map { speed -> speed > 60 } // double boolean
.distinctUntilChanged()
.filter { aboveLimit -> aboveLimit == true }
.subscribe { writeTicket(car) }
}
}
private fun writeTicket(car: Car) {
// do some stuff
}
}
