iteration.kt

val treeSet = TreeSet<Int>()
val treeSetDescending = TreeSet<Int>(Collections.reverseOrder())
val hashSet = HashSet<Int>()
val random = Random()
repeat(10) {
    val number = random.nextInt(100)
    treeSet.add(number)
    treeSetDescending.add(number)
    hashSet.add(number)
} 

println("sorted: $treeSet") // sorted: [5, 12, 31, 41, 56, 58, 76, 84, 89, 98]
println("sorted descending: $treeSetDescending") // sorted descending: [98, 89, 84, 76, 58, 56, 41, 31, 12, 5]
println("not sorted: $hashSet") // not sorted: [98, 84, 5, 56, 89, 41, 58, 12, 76, 31]