Crazy Kotlin lecture series on Flow control – Sequence structure and branch structure III

4.2.4 When expression

fun main(args: Array<String>){

var score = ‘B’

val str = when (score) {

‘A’ -> {

Println (” Hope you can make more progress “)

“Good”

}

‘B’ -> {

Println (” You don’t know what you’re capable of until you put it together “)

“Good”

}

‘C’ -> ‘middle’

‘D’ -> “Pass”

else -> {

Println (” Say nothing, come again “)

“Fail”

}

}

println(str)

}

4.2.5 When branch handles scope

fun main(args: Array<String>){

val age = java.util.Random().nextInt(100)

println(age)

// Assign a value to STR using the when expression

var str = when (age){

in 10.. 25 -> “I was young at that time”

in 26.. 50 -> “Scenery vaguely reminiscent of last year”

in 51.. 80 -> “Drunk to hear the sound of the orchestra”

Else ->”

}

println(str)

}

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4.2.6 When branch processing type

fun main(args: Array<String>){

var inputPrice = 26

println(realPrice(inputPrice))

}

// The program determines the type of inputPrice

fun realPrice(inputPrice: Any) = when(inputPrice){

// If inputPrice is of type String, the program returns a Double converted from that String

is String -> inputPrice.toDouble()

// If inputPrice is of type Int, the program returns a Double converted from that Int

is Int -> inputPrice.toDouble()

is Double -> inputPrice

The else – > 0.0

}

4.2.7 When conditional branch

The when branch can also be used to replace if… Else if chain, in which case there is no need to provide any conditional expression for the WHEN branch, in which case each branch condition is a Boolean expression, and the branch is executed when the specified branch’s Boolean expression is true. For example, the following code.

fun main(args: Array<String>){

Val ln = readLine()// ln is String? Type, so you need to check whether ln is null

if(ln ! = null){

// The when branch does not require any conditional expressions

when {

// Each branch condition is a Boolean expression

Matches (Regex(“\\d+”)) -> println(” You entered all numbers “)

Ln. Matches (Regex ([a zA – Z] + “”)) – > println (” you input all the letters”)

Ln. Matches (Regex (” [a zA – Z0-9] +)) – > println (” the letters and Numbers you entered “)

Else -> println(” Your input contains special characters “)

}

}

}

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