Data Types Workbook
Eleven short exercises on Kotlin's basic types — val and var, the number types, explicit conversions, strings and templates, nullability, and Unit and Nothing.
Kotlin Workbooks
Short coding exercises to practice the concepts from each Kotlin lesson.
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Functions Workbook
Fifteen short exercises on Kotlin functions — single-expression bodies, default and named arguments, vararg, and top-level and local functions. Solutions reveal on click.
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Control Flow Workbook
Eleven short exercises on Kotlin control flow — if as an expression, ranges, for loops, membership with in, indices, and labelled break.
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when Workbook
Ten short exercises on Kotlin's when — as a statement and an expression, with and without a subject, range and type matching, multiple values per branch, and exhaustiveness.
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Smart Casts Workbook
Ten short exercises on Kotlin smart casts — is and !is, null-check narrowing, smart casts in when, combined conditions, early returns, and where they don't apply.
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Null Safety Workbook
Ten short exercises on Kotlin null safety — safe calls, the Elvis operator, !!, safe casts, ?.let, lateinit, nullable collections, and platform types.
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Collections Workbook
Eleven short exercises on Kotlin collections — read-only versus mutable, the factory functions, map access, getOrDefault, the plus and minus operators, and read-only signatures.
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Lambdas Workbook (Part 1): The Basics
Twelve short exercises on the lambda basics — defining and calling, parameters and results, function types, the implicit it, and multi-line bodies.
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Lambdas Workbook (Part 2): The Collection API
Thirteen short exercises on lambdas at work — forEach, the trailing-lambda convention, map and filter, chaining, the any/all/count/find/sumOf toolkit, and writing your own higher-order function.
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Lambdas Workbook (Part 3): Closures
Eleven short exercises on closures — capturing parameters, capturing and mutating a var, returning a stateful lambda, shared state, and capturing a loop variable.
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Lambdas Workbook (Part 4): References, Returns, and Anonymous Functions
Twelve short exercises on the four kinds of function reference, non-local returns and labels, and anonymous functions.
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Lambdas Workbook (Part 5): inline and Receivers
Eleven short exercises on inline functions and lambdas with a receiver — marking a function inline, reified, receiver lambda types, apply and buildString, and writing a receiver-based builder.
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Classes Workbook (Part 1)
Eleven short exercises on Kotlin classes — declarations, primary constructors, properties, init blocks, custom accessors, encapsulation, and inheritance.
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Class Types Workbook (Part 2)
Ten short exercises on Kotlin's specialized classes — data classes, enums, sealed hierarchies, objects and companions, inner classes, and value classes.
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Enums Workbook
Ten short exercises on Kotlin enums — constants, exhaustive when, constructor properties, methods, per-constant overrides, the built-in members, and implementing interfaces.
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Interfaces Workbook
Ten short exercises on Kotlin interfaces — implementing them, default methods, property contracts, resolving clashes between defaults, functional interfaces, and interface inheritance.
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Extension Functions Workbook
Ten short exercises on Kotlin extensions — declaring extension functions and properties, the receiver, static resolution, nullable receivers, and members winning over extensions.
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Equality Workbook
Ten short exercises on Kotlin equality — structural == versus referential ===, null-safe comparison, data-class equals and hashCode, and Comparable with the comparison operators.
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Destructuring Workbook
Ten short exercises on Kotlin destructuring — declarations, the componentN convention, data classes, map entries, withIndex, lambda parameters, skipping with underscore, and custom components.
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Visibility Workbook
Ten short exercises on Kotlin visibility — the default, private and protected, the module-scoped internal, private setters, private constructors, and file organization.
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Delegation Workbook
Nine short exercises on Kotlin delegation — class delegation with by, lazy and observable properties, map-backed properties, writing a custom delegate, and lateinit versus lazy.
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Generics Workbook
Nine short exercises on Kotlin generics — generic functions and classes, declaration-site variance with out and in, star projections, and reified type parameters.
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Exceptions Workbook
Ten short exercises on Kotlin exception handling — try/catch as an expression, require and check, use for resources, runCatching and Result, Nothing, and sealed result types.
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Java Interop Workbook
Ten short exercises on Kotlin/Java interop — getters as properties, platform types, SAM conversion, and the @Jvm annotations that make Kotlin pleasant to call from Java.
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Scope Functions Workbook
Ten short exercises on Kotlin's scope functions — let, run, with, apply, and also, decided by receiver-versus-parameter and result-versus-object, plus takeIf and takeUnless.
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Operator Overloading Workbook
Ten short exercises on Kotlin operator overloading — plus, get and set, invoke, contains, compareTo, compound assignment, unaryMinus, and making a type iterable.
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Coroutines Workbook
Nine short exercises on Kotlin coroutines — suspend functions, suspension points, launch, async and await, coroutineScope, structured concurrency, and dispatchers.