Solution to Java to Kotlin Conversion Quiz

solution.kts

import java.io.BufferedReader
import java.io.File
import java.io.FileReader
import java.io.IOException


//Java to Kotlin Conversion Quizz samples for Java Magazine

//Example 1: Statics
object MySingleton {
  private const val state: Int = 42
}

//Example 2: Functions / Primitive/Object conversion hell
fun convert(value: String): String {
  return value
      .map { it.toInt() }
      .joinToString { Integer.toBinaryString(it) }
}

val result = convert("Welcome2Java'sPrimitive2ObjectHell")

println(result)

//Example 3: Nullability
var firstFileInParentFolder = File("/tmp")
    ?.parentFile?.listFiles()?.get(0)?.name
    ?: "unknown"

//Example 4: Extension methods
fun String.printFile() {
  try {
    BufferedReader(FileReader(this)).use { br ->
      var line: String?
      while (br.readLine().also { line = it } != null) {
        println(line)
      }
    }
  } catch (e: IOException) {
    e.printStackTrace()
  }
}

"foo.txt".printFile()

//Example 5: Collections
val characterCount: Map<Char, Int> = listOf("Count", "us", "all")
    .joinToString().groupingBy { it }.eachCount()

Based on this quiz, some notes:

• example 1 was obvious, an object in Kotlin is a singleton class
• example 2: wasn't clear if the function signature with the converter function as parameter should be kept, I didn't do it because the type differences between Java and Kotlin was a bit annoying
• example 3: kotlin thinks a File does not return a null value, but I'm not sure
• example 4: I created an extension method, like the comment suggested, but I'm not sure what the power of Kotlin is here exactly
• example 5: nice one!