📌 when Expression in Kotlin

In Kotlin, the when expression is a more powerful and flexible version of the traditional switch statement found in other languages. It is often used to replace multiple if-else-if statements for cleaner and more readable code.

✅ Syntax of when

kotlin
val number = 5when (number) {    1, 2, 3 -> println("Small Number")    4, 5, 6 -> println("Medium Number")    else -> println("Large Number")}

Output:

mathematica
Medium Number

✅ 3. Using Ranges and Conditions

when supports range checks using the in and !in operators.

kotlin
val age = 25when (age) {    in 0..12 -> println("Child")    in 13..19 -> println("Teenager")    in 20..59 -> println("Adult")    else -> println("Senior")}

Output:

nginx
Adult

✅ 4. Using when Without an Argument

You can use when without an argument by using Boolean conditions.

kotlin
val number = 15when {    number % 2 == 0 -> println("Even Number")    number % 2 != 0 -> println("Odd Number")    else -> println("Unknown")}

Output:

javascript
Odd Number

✅ 5. Using when as an Expression

when can return a value directly.

kotlin
val grade = 'B'val result = when (grade) {    'A' -> "Excellent"    'B' -> "Good"    'C' -> "Average"    else -> "Fail"}println("Result: $result")

Output:

makefile
fun (obj: Any) {    Unknown Type

✅ 7. Smart Casting in when

Kotlin performs smart casting inside when if it recognizes a type.

kotlin
fun (obj: Any) {    when (obj) {        is String -> println("Length: ${obj.length}")        is Int -> println("Double Value: ${obj * 2}")        else -> println("Unknown")    }}describe("Hello")describe(7)

Output:

vbnet
Length: 5Double Value: 14

✅ Conclusion

• when is more readable and powerful than traditional switch.

• Supports multiple conditions, ranges, and type checking.

• Can be used as an expression to return a value.

• Eliminates the need for repetitive if-else statements.