Kotlin: implement switch-case statement in Kotlin

Kotlin Programming

Question or issue of Kotlin Programming:

How to implement equivalent of following Java switch statement code in Kotlin?

switch (5) {
    case 1:
    // Do code
    break;
    case 2:
    // Do code
    break;
    case 3:
    // Do code
    break;
}

How to solve this issue?

Solution no. 1:

You could do like this:

when (x) {
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> { // Note the block
        print("x is neither 1 nor 2")
    }
}

extracted from official help

Solution no. 2:


When Expression
when replaces the switch operator of C-like languages. In the simplest form it looks like this
when (x) {
1 -> print(“x == 1”)
2 -> print(“x == 2”)
else -> { // Note the block
print(“x is neither 1 nor 2”)
}
}

when matches its argument against all branches sequentially until some branch condition is satisfied. when can be used either as an expression or as a statement. If it is used as an expression, the value of the satisfied branch becomes the value of the overall expression. If it is used as a statement, the values of individual branches are ignored. (Just like with if, each branch can be a block, and its value is the value of the last expression in the block.)

From https://kotlinlang.org/docs/reference/control-flow.html#when-expression

Solution no. 3:

switch in Java is effectively when in Kotlin. The syntax, however, is different.

when(field){
    condition -> println("Single call");
    conditionalCall(field) -> {
        print("Blocks");
        println(" take multiple lines");
    }
    else -> {
        println("default");
    }
}

Here’s an example of different uses:

// This is used in the example; this could obviously be any enum. 
enum class SomeEnum{
    A, B, C
}
fun something(x: String, y: Int, z: SomeEnum) : Int{
    when(x){
        "something" -> {
            println("You get the idea")
        }
        else -> {
            println("`else` in Kotlin`when` blocks are `default` in Java `switch` blocks")
        }
    }

    when(y){
        1 -> println("This works with pretty much anything too")
        2 -> println("When blocks don't technically need the variable either.")
    }

    when {
        x.equals("something", true) -> println("These can also be used as shorter if-statements")
        x.equals("else", true) -> println("These call `equals` by default")
    }

    println("And, like with other blocks, you can add `return` in front to make it return values when conditions are met. ")
    return when(z){
        SomeEnum.A -> 0
        SomeEnum.B -> 1
        SomeEnum.C -> 2
    }
}

Most of these compile to switch, except when { ... }, which compiles to a series of if-statements.

But for most uses, if you use when(field), it compiles to a switch(field).

However, I do want to point out that switch(5) with a bunch of branches is just a waste of time. 5 is always 5. If you use switch, or if-statements, or any other logical operator for that matter, you should use a variable. I’m not sure if the code is just a random example or if that’s actual code. I’m pointing this out in case it’s the latter.

Solution no. 4:

The switch case is very flexible in kotlin

when(x){

    2 -> println("This is 2")

    3,4,5,6,7,8 -> println("When x is any number from 3,4,5,6,7,8")

    in 9..15 -> println("When x is something from 9 to 15")

    //if you want to perform some action
    in 20..25 -> {
                 val action = "Perform some action"
                 println(action)
    }

    else -> println("When x does not belong to any of the above case")

}

Solution no. 5:

Just use the when keyword. If you want to make a loop, you can do like this:

var option = ""
var num = ""

    while(option != "3") {
        println("Choose one of the options below:\n" +
                "1 - Hello World\n" +
                "2 - Your number\n" +
                "3 - Exit")

        option = readLine().toString()

// equivalent to switch case in Java //

        when (option) {
            "1" -> {
                println("Hello World!\n")
            }
            "2" -> {
                println("Enter a number: ")
                num = readLine().toString()

                println("Your number is: " + num + "\n")
            }
            "3" -> {
                println("\nClosing program...")
            }
            else -> {
                println("\nInvalid option!\n")
            }
        }
    }

Solution no. 6:

Here is an example to know Using “when” with arbitrary objects,

VehicleParts is a enum class with four types.

mix is a method which accepts two types of VehicleParts class.

setOf(p1, p2) – Expression can yield any object

setOf is a kotlin standard library function that creates Set containing the objects.

A set is a collection for which the order of items does not matter.
Kotlin is allowed to combine different types to get mutiple values.

When I pass VehicleParts.TWO and VehicleParts.WHEEL, I get “Bicycle”.
When I pass VehicleParts.FOUR and VehicleParts.WHEEL, I get “Car”.

Sample Code,

enum class VehicleParts {
TWO, WHEEL, FOUR, MULTI
}

fun mix(p1: VehicleParts, p2: VehicleParts) =
when (setOf(p1, p2)) {

    setOf(VehicleParts.TWO, VehicleParts.WHEEL) -> "Bicycle"

    setOf(VehicleParts.FOUR, VehicleParts.WHEEL) -> "Car"

    setOf(VehicleParts.MULTI, VehicleParts.WHEEL) -> "Train"
    else -> throw Exception("Dirty Parts")

}

println(mix(VehicleParts.TWO,VehicleParts.WHEEL))

Solution no. 7:

        val operator = '+'
        val a = 6
        val b = 8

        val res = when (operator) {
            '+' -> a + b
            '-' -> a - b
            '*' -> a * b
            '/' -> a / b
            else -> 0
        }
        println(res);

We use the following code for common conditions

        val operator = '+'
        val a = 6
        val b = 8

        val res = when (operator) {
            '+',
            '-' -> a - b
            '*',
            '/' -> a / b
            else -> 0
        }
        println(res);

Hope this helps!