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Kotlin If and Else

Choose a notice and keep it as the result of an expression.

How it works

Kotlin if can be an expression, so each branch can provide a value. An expression needs an else branch when all paths must produce a result. Put rejected input before ordinary success cases so the meaning of the remaining branches stays simple.

Run this Kotlin example

These are local Kotlin/JVM programs. Install a JDK and the compiler using the official Kotlin compiler guide, or use an IDE with Kotlin support. Check java -version and kotlinc -version in a new terminal. The reviewed compiler is Kotlin 2.4.21 with a JVM 21 target, executed on Temurin JDK 25.0.5. Use JDK 21 or newer for this target. Android, Kotlin/JS and Kotlin/Native require separate platform projects and are not the tested environment here.

Save the complete source as if-else.kt in its own learning folder. The package line gives this example a namespace, not a network address. Bhylu has no Kotlin browser runner; do not use the JavaScript or Python editor. Apache, PHP and MySQL are not required.

Compile with kotlinc if-else.kt -jvm-target 21 -include-runtime -d lesson.jar, then run java -jar lesson.jar. Use a learning folder you own and keep generated JARs outside the website. These sources require no third-party application libraries.

Download the complete if-else.kt · Download all source files with hash checks

For the optional collection, save download-examples.mjs in a new learning folder and run node download-examples.mjs. A local preview uses node download-examples.mjs http://127.0.0.1:8000/examples/kotlin/. It refuses an existing bhylu-kotlin-examples folder and installs or executes no Kotlin code. Compile one ordinary lesson at a time by filename.

Example

if-else.kt

package bhylu.lessons.k_if_else

fun main() {
    val available = 3
    val notice = if (available < 0) "Invalid count" else if (available == 0) "No bicycles ready" else "Ready to hire"
    println(notice)
}

Expected result

Ready to hire

The result is assigned once to notice. The negative case is kept separate from the valid empty case. No separate mutable placeholder is needed before the decision.

For exact language and library contracts, consult the official Kotlin documentation. These fictional fixtures are learning programs, not a deployed hire service.

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