References
Kotlin reference
Write concise, typed code for JVM applications.
Kotlin Basics
Use values and string templates.
Kotlin Lists
Process an ordered collection.
Kotlin Functions
Declare typed parameters and a return type.
Kotlin when Expressions
Choose a result from several conditions with when.
Kotlin null safety
Distinguish nullable from non-null types, and use ?., ?:, let, and !! deliberately.
Kotlin collections and higher-order functions
Filter, map, group, sort, and fold lists with lambdas instead of loops.
Kotlin Classes
Declare a class with a primary constructor and private state.
Kotlin data classes and sealed interfaces
Model alternatives with a sealed hierarchy and let the compiler check that every case is handled.
Kotlin object, companion object, and delegation
Create singletons, class-level factories with private constructors, and reuse behaviour by delegating to an interface.
Kotlin sorting and binary search
Sort lists with sorted and sortedBy, and find a value or its insertion point with binarySearch.
Kotlin ArrayDeque as a stack and a queue
Check balanced brackets with a stack and serve items in arrival order with a queue.
Kotlin maps: counting and indexing
Count words with groupingBy and build a lookup map with getOrPut.
Kotlin unit tests with lambdas and runCatching
Write a minimal test function that reports passes and failures, including expected exceptions.
Kotlin SHA-256 and PBKDF2 on the JVM
Hash text with MessageDigest and derive a salted password hash with PBKDF2.
Kotlin threads, AtomicInteger, and an executor
Start threads that update a shared counter safely and split a sum across a thread pool.