import com.fasterxml.jackson.databind.ObjectMapper

fun main ( args : Array < String > ) {

    val mapper = ObjectMapper()
    val jsonResult = mapper.writerWithDefaultPrettyPrinter()
            .writeValueAsString(someString)

    System.out.println("blank: ${jsonResult.isBlank()}")
    System.out.println("isEmpty: ${jsonResult.isEmpty()}")
    System.out.println("{}: ${jsonResult.contentEquals("{}")}")



}

jsonResult

{}

{}

false

isEmpty

isBlank

instanceof

typeof

Files

sequenceOf(1L, 2L, 3L).map { it + 1L }.forEach { println(it) }

// The below code results in a compilation error
data class ViewModel(
    var lineSpeed: Int? = null
)

val viewModel = ViewModel()

if(viewModel.lineSpeed != null && viewModel?.lineSpeed > 0 ) {}

//Error : Smart cast to 'Int' is impossible, because 'viewModel.lineSpeed' is a mutable property that could have been changed by this time

fun <K, V> Map<K, V?>.filterValuesNotNull() = filterValues { it != null } as Map<K, V>

JDK_16="C:\\Program Files\\Java\\jdk1.6.0_45"
JDK_17="C:\\Program Files\\Java\\jdk1.7.0_80"
JAVA_HOME="C:\\Program Files\\Java\\jdk1.8.0_172"
JDK_9="C:\\Program Files\\Java\\jdk-9.0.4"

name

B

String

String?

open class A(val name: String?)
class B(name: String) : A(name)
fun findName(b: B): String = b.name // errors because `b.name` is `String?`

fun findCombs(res: List<String>, digis: List<Int>) : List<String> = if (digitss.isEmpty()) res 
        else for (letter in map[digis[0]]) findCombs(res + letter, digis.subList(1, digis.lastIndex))