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Kotlin track: IntermediateMission: IntermediateNullable typesSafe callsElvis operator

Before you start this intermediate track

Functions and collections. Read lambdas, nullable values, and conditional expressions.

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LEARN THE CONCEPT

Understand it, then try it.

A postcard can have an optional nickname. The question mark in String? permits null. A safe call with ?. runs uppercase only when the nickname exists. The Elvis operator ?: supplies FRIEND if that result is null. A present name is preserved and formatted; a missing name gets a readable greeting.

Main.kt

1fun main() {2    val nickname: String? = null3    val greeting = nickname?.uppercase() ?: "FRIEND"4    println("Hello, $greeting!")5}

Each mission is a complete independent Kotlin/JVM program with its own main function. Run it with Kotlin 1.9 or later in a Kotlin playground or a configured Kotlin/JVM project. No Android APIs are required.

Track the values line by line. Predict the result before running this example in your own editor.

Read the official language documentation

kotlinlang.org/docs/collection-filtering.html kotlinlang.org/docs/null-safety.html kotlinlang.org/docs/control-flow.html