how to change nested if-else to when statements using Kotlin? - kotlin

Question

I have the following block of code and want to reduce it using Kotlin. How can I do that?
if (name == nameArray[0]) {
// The statement
} else if(name == nameArray[1]) {
// The statement
} else if(name == nameArray[2]) {
// The statement
} else if(name == nameArray[3]) {
// The statement
} else {
// The statement
}

Answer 1

If the array is small and you want to map an action to each index:
You could use indexOfFirst to determine the smallest index which meats your condition. Then you can use a when statement to decide what to do.
when(nameArray.indexOfFirst{ it == name }) {
0 -> // do something
1 -> // do something else
//...
else -> // do something different
}
In case you might want to do the same thing for multiple indices you can use comma separated values. In case the indices are consecutive, you can use ranges:
when(nameArray.indexOfFirst{ it == name }) {
0 -> // do something
1, 2 -> // do the same thing for 1 and 2
in 3..6 -> // do the same thing for 3, 4, 5 and 6
//...
else -> // do something different
}
In order to use this syntax it is a good idea to do index retrieval (like shown) first.
If the array is big and you really only want to check for specific elements:
when(name) {
nameArray[0] -> // do something
nameArray[1] -> // do something
nameArray[2] -> // do something
nameArray[3] -> // do something
else -> // other action
}

Answer 2

You can use when to simplify it as below
when(name) {
nameArray[0] -> //statement
nameArray[1] -> //statement
nameArray[2] -> //statement
nameArray[3] -> //statement
else -> //statement
}
Alternatively, if you can use an enum instead of the nameArray as below
enum class Names {
NAME_1, NAME_2, NAME_3
}
And have name of the Names enum type, you can then use the when clause as below, which is a cleaner way and is more readable
when(name) {
Names.NAME_1 -> //statement
Names.NAME_2 -> //statement
Names.NAME_3 -> //statement
}

Answer 3

You can use a better and more powerful Kotlin construct, when.
It works similarly to switch-case constructs but you can use expression too, check here for more.
Specific to your example you may write:
when (name) {
nameArray[0] -> {
//The statement
}
nameArray[1] -> {
//The statement
}
nameArray[2] -> {
//The statement
}
nameArray[3] -> {
//The statement
}
else -> {
//Executes when conditions are not met
}
}

Answer 4

Maybe I'm misinterpreting what you want to do, but in my opinion a when statement is over-complicating this. In your original code you just want to determine if the array contains the name value in any of the indices from 0 to 3 and respond accordingly.
if ((nameArray.indexOfFirst(name::equals) in 0..3) {
// The statement
} else {
// The else branch
}

Answer 5

Shorter way: Iterate the array instead of if-else every possible index of the array:
fun main(args: Array<String>) {
val nameArray: Array<String> = arrayOf("naam", "nombre", "name", "Name")
val name: String = "name";
for (i in 0..(nameArray.size - 1)) {
if (name == nameArray[i]) {
println("The statement should be executed on index " + i)
}
}
}
Output:
The statement should be executed on index 2