How to implement switch-case statement in Kotlin - kotlin

Question

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;
}

Answer 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

Answer 2

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.

Answer 3

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")
}

Answer 4

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

Answer 5

when defines a conditional expression with multiple branches. It is similar to the switch statement in C-like languages. Its simple form 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 first matching 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.
import java.util.*
fun main(args: Array<String>){
println("Hello World");
println("Calculator App");
val scan=Scanner(System.`in`);
println("""
please choose Your Selection to perform
press 1 for addition
press 2 for substraction
press 3 for multipication
press 4 for divider
press 5 for divisible
""");
val opt:Int=scan.nextInt();
println("Enter first Value");
val v1=scan.nextInt();
println("Enter Second Value");
val v2=scan.nextInt();
when(opt){
1->{
println(sum(v1,v2));
}
2->{
println(sub(v1,v2));
}
3->{
println(mul(v1,v2));
}
4->{
println(quotient(v1,v2));
}
5->{
println(reminder(v1,v2));
}
else->{
println("Wrong Input");
}
}
}
fun sum(n1:Int,n2:Int):Int{
return n1+n2;
}
fun sub(n1:Int, n2:Int):Int{
return n1-n2;
}
fun mul(n1:Int ,n2:Int):Int{
return n1*n2;
}
fun quotient(n1:Int, n2:Int):Int{
return n1/n2;
}
fun reminder(n1:Int, n2:Int):Int{
return n1%n2;
}

Answer 6

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")
}
}
}

Answer 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);

Answer 8

In kotlin, their is no switch-case statement. But we have when expression similar to switch. Just like if-else or switch, first all conditions are checked, if none matches then else code evaluated.
when (n) {
1 -> {
print("First")
// run your code
}
2 -> print("Second")
3, 4 -> print("Third or Forth") // check multiple conditions for same code
in 1..100 -> print("Number is in the range")
else -> {
print("Undefined")
}
}
There is no need of any break as of switch case.

Answer 9

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))

Answer 10

If You want to print or open multiple Activities using switch case (When) in Kotlin then use this code.. Thank you..
var dataMap: Map<String?, String?> = HashMap()
var noteType: String? = ""
when (noteType) {
"BIGTEXT" -> NEW_PAGE(dataMap)
"NORMAL" -> NORMAL_PAGE(dataMap)
"ABOUT"->ABOUT_PAGE((dataMap))
}