Returns, Jumps and Labels in Kotlin

Kotlin is a statically typed, general-purpose programming language developed by JetBrains, that has built world-class IDEs like IntelliJ IDEA, PhpStorm, Appcode, etc. It was first introduced by JetBrains in 2011 and a new language for the JVM. Kotlin is an object-oriented language, and a “better language” than Java, but still be fully interoperable with Java code. As the Kotlin says: Kotlin has three structural jump expressions as follow:

1. return
2. break
3. continue

These can be a part of the large expression as Kotlin say. So, let’s start with “return”.

1. return

It’s a statement that generally we use in functions during declaration for returning the values after execution of a function. By default it returns from the nearest enclosing function or anonymous function. Let’s take an example,

Example:

Kotlin

fun add(a:Int,b:Int) : Int {
   // ans having final value after execution
   val ans = a + b
   // here we have returned it
   return ans
 }
 fun main(args: Array<String>) {

    val first: Int = 10
    val second: Int = 20
    // called function and
    // Collected the returned value in sum
    val sum = add(first,second)
    println("The sum is: $sum")
}

Another use of return

Kotlin

fun GfG() {
    listOf(1, 2, 3, 4, 5).forEach {
        // non-local return directly
          // to the caller of GfG()
        if (it == 3) return
        print(it)
    }
    println("this point is unreachable")
}

So, that’s how the return statement work.

2. Jumps & labels

2.1. break

A break statement is used to terminate the flow of a loop. but only terminates the nearest enclosing loop i.e. if you are having two nested for-loops and the break statement is present in the inner for-loop then the inner for-loop will be terminated first and after that, if another break is added then the outer for-loop will also be terminated.

Example:

Kotlin

fun main(args : Array<String>){
    for(ch in 'A'..'C'){    // Outer loop
        for (n in 1..4){     // Inner loop
            println("processing...")
            if(n == 2)     // it will terminate Inner loop
                break
        }
        if(ch == B)
            break     // but it will terminate Outer loop
    }
}

We can also optimize the above code or reduce the line of code as well, using labels. 

2.2. labels

Any expression in Kotlin may be marked with a label. Labels have the form of an identifier followed by the @ sign, such as name@ or xyz@. To label an expression, just add a label in front of it.

Example:

Kotlin

fun main(args : Array<String>){
   Outerloop@ for(ch in 'A'..'C'){    // Outer loop
        for (n in 1..4){     // Inner loop
            println("processing...")
            if(n == 2)     // it will terminate Outerloop directly
                break@Outerloop
        }
        // here we don't need it
       /*
         if(ch==B)
                break
        */
    }
}

2.3. continue

It is the same as the break statement but the only difference is, the break statement terminates the whole iteration of a loop whereas continuing skips the current iteration and we can use labels here as well. 

Example:

Kotlin

fun main(args: Array<String>) {
    // outerloop is label name
    outerloop@ for (i in 1..5) {
        for (j in 1..4) {
            if (i == 3 || j == 2)
                // here we have used that
                continue@outerloop
            println("Happy Diwali!")
        }
    }
}

That’s all about return, jump, and labels.