Kotlin is more than the language Android applications happen to use. Its type system, null safety, delegates, properties, extension functions, coroutines, and other language features influence how Android code is designed and maintained.

The goal is not to memorise Kotlin keywords or every language feature. It is to understand why those features exist, what problems they solve, and the trade-offs they introduce in production code.

What this section builds

The questions are arranged so later concepts build on earlier ones. Together they develop a mental model of Kotlin as a language rather than a collection of syntax, covering topics such as immutability, object initialisation, delegation, type hierarchies, null safety, and language features commonly used throughout Android development.

Use the interview-ready answer first, then go deeper only where you need more context. By the end of this section, you should be able to explain not only what a Kotlin feature does, but also when you would choose it and why it improves production code.

Questions

• What is the difference between val, var, and const val?
• What is the difference between lateinit and lazy?
• What is the difference between Any, Unit, and Nothing?