If, When, and While

Branching and looping are common operations in most programming languages. Most languages have some concept of if (branch based on a condition) and while (loop based on a condition). Kotlin has its takes on those control structures, plus a when structure that is a bit reminiscent of things like Java’s switch structure.

So, let’s take a look at if, when, and while, and see how Kotlin handles them the same as — and in some cases, differently than — other languages.

If

if is nearly ubiquitous in computer programming, whether that is Java:

if (i>10) {
  // do something
}
else {
  // do something else
}

…JavaScript:

if (i>10) {
  // do something
}
else {
  // do something else
}

// yes, it is the same as the Java syntax

…or Ruby:

if (i>10)
  # do something
else
  # do something else
end

On the surface, a Kotlin if works the same way:

  val i = 3

  if (i > 10) {
    println("something")
  }
  else {
    println("something else")
  }

As with most languages, the else clause is optional, if you do not have anything special that you want to do in that situation:

  val i = 3

  if (i > 10) {
    println("something")
  }

  println("the if is done")

For single-line conditional work, you can skip the braces:

  val i = 3

  if (i>10) println("something") else println("something else")

if also supports else if in addition to a simple else:

  val i = 3

  if (i > 10) {
    println("something")
  }
  else if (i > 2) {
    println("something else")
  }
  else {
    println("and now for something completely different")
  }

However, as you will see in the next section, the convention in Kotlin development is to use when instead of if for such scenarios.