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Kotlin Fundamentals Flashcards

Kotlin — Fundamentals Flashcards

30 interactive flashcards covering core Kotlin concepts from null safety to inline functions. Press Space to flip, rate 1-4.

Additional Flashcard Topics

  • Null Safety: String? is nullable; String is non-nullable. The compiler enforces null checks: ?. (safe call), ?: (elvis operator), !! (force unwrap — dangerous).

  • Data Classes: data class User(val name: String, val age: Int) auto-generates equals, hashCode, toString, copy, and destructuring.

  • Sealed Classes: restricted class hierarchies. All subclasses are known at compile time, enabling exhaustive when expressions.

  • Extension Functions: fun String.isEmail() = ... — add methods to existing types without modifying them. Resolved statically (not polymorphic).

  • Coroutines: suspend functions, launch, async, withContext. Lightweight concurrency; coroutines are multiplexed onto threads by the runtime.

  • Delegation: by lazy { ... } for lazy initialization; by observable { ... } for change notification; custom delegates via ReadOnlyProperty/ReadWriteProperty.

Intuition

Kotlin is a modern JVM language that combines object-oriented and functional programming. Null safety is enforced at the type level — the compiler prevents null pointer exceptions by making nullable types explicit. Coroutines provide lightweight concurrency without callback hell, and inline functions eliminate the overhead of passing lambdas by inlining the lambda body at the call site. Data classes auto-generate equals, hashCode, toString, and copy methods. Kotlin is fully interoperable with Java — you can use Java libraries from Kotlin and vice versa.

Common Pitfalls

  • var vs val misuse: Using var when val suffices makes code harder to reason about — prefer immutability and only use var when reassignment is truly needed.
  • Scope function confusion: let, run, with, apply, and also differ in context object (this vs it) and return value — mixing them up leads to unreadable code.
  • Coroutine dispatcher selection: Running CPU-bound work on Dispatchers.Main freezes the UI; running IO-bound work on Dispatchers.Default wastes CPU threads — match the dispatcher to the work type.
  • Confusing is and as: is checks type (with smart cast); as casts (throws ClassCastException on failure). Use as? for safe casting.
  • Inline function overhead: inline eliminates lambda allocation but can increase code size. Use noinline for parameters that shouldn’t be inlined.

Cross-References

  • Swift Basics: Null safety and protocol-oriented patterns compared across languages.
  • Java Basics: Kotlin runs on the JVM; understanding Java helps with Kotlin interop.
  • Dart Basics: Null safety and async patterns compared across languages.