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Kotlin Variables

Use val for a stable binding and var when reassignment is part of the task.

How it works

A variable has a type even when the compiler infers it. val prevents reassignment of the binding, while var allows a later value of a compatible type. A val reference can still refer to a mutable object, so it does not guarantee deep immutability.

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 variables.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 variables.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 variables.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

variables.kt

package bhylu.lessons.k_variables

fun main() {
    val desk = "Canal Gate"
    var available = 6
    available -= 2
    println("$desk: $available")
}

Expected result

Canal Gate: 4

The desk label stays fixed while availability changes. Prefer val by default because fewer moving values make a calculation easier to inspect; use var when the update is intentional.

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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