61. String Formatting

Kotlin exposes Java’s printf-style formatting through the format extension on String, plus padding and joining helpers that cover most everyday needs.

fun main() {
    val pi = 3.14159
    println("%.2f".format(pi))          // two decimal places
    println(String.format("%05d", 42))   // zero-padded width 5
    println("%-8s|".format("left"))      // left-justified in width 8
    println("%8s|".format("right"))      // right-justified in width 8
}

For non-numeric alignment, padStart and padEnd pad a string to a target length with a chosen character. joinToString builds a single string from a collection with a separator, prefix, and postfix.

println("7".padStart(3, '0'))
println("hi".padEnd(5, '.') + "|")

val nums = listOf(1, 2, 3)
println(nums.joinToString(separator = ", ", prefix = "[", postfix = "]"))

Running it:

$ kotlin run
3.14
00042
left    |
   right|
007
hi...|
[1, 2, 3]

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