Compare Kotlin's when with Java's switch?

Overview

when

switch

Comparison Table

Basic Comparison

Java switch

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String result;
switch (status) {
    case SUCCESS:
        result = "Success";
        break;
    case ERROR:
        result = "Error";
        break;
    default:
        result = "Unknown";
}

Kotlin when (Expression)

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val result = when (status) {
    Status.SUCCESS -> "Success"
    Status.ERROR -> "Error"
    else -> "Unknown"
}

Advanced Features

Ranges

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when (score) {
    in 90..100 -> "A"
    in 80..89 -> "B"
    in 70..79 -> "C"
    else -> "F"
}

Type Checks

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when (obj) {
    is String -> println(obj.length) // Smart cast
    is Int -> println(obj * 2)
    else -> println("Unknown")
}

Multiple Conditions

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when (x) {
    1, 2, 3 -> println("Small")
    in 4..10 -> println("Medium")
    else -> println("Large")
}

Without Argument

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when {
    x > 0 -> println("Positive")
    x < 0 -> println("Negative")
    else -> println("Zero")
}

Sealed Classes

kotlinCopy
sealed class Result {
    data class Success(val data: String) : Result()
    data class Error(val message: String) : Result()
}

fun handle(result: Result) = when (result) {
    is Result.Success -> result.data
    is Result.Error -> result.message
    // No else needed - exhaustive!
}

Java 14+ Enhanced Switch

javaCopy
String result = switch (status) {
    case SUCCESS -> "Success";
    case ERROR -> "Error";
    default -> "Unknown";
};

Advantage: Kotlin's

textCopy

when

is more powerful and type-safe than Java's

textCopy

switch

.