Kotlin

Getting Started

1. What is Kotlin?What Kotlin is, why Google made it Android's preferred language, and where else it shows up today.
2. Variables — val and varKotlin's two ways to declare a variable, and why you should reach for val by default.
3. Basic Types and Type InferenceKotlin's core types and how the compiler figures out most of them without annotations.

Strings & Null Safety

1. String TemplatesEmbedding variables and expressions directly inside strings instead of concatenating pieces by hand.
2. Nullable TypesHow Kotlin's type system distinguishes values that can be null from values that never can, catching a huge class of bugs at compile time.
3. Safe Calls and the Elvis OperatorThe ?. and ?: operators that let you work with nullable values concisely instead of writing a null check every time.
4. The Not-Null Assertion (!!)Kotlin's escape hatch for bypassing null checks, and why reaching for it usually means reaching for the wrong tool.

Control Flow

1. if as an ExpressionWhy Kotlin's if can produce a value directly, removing a whole category of temporary-variable boilerplate.
2. The when ExpressionKotlin's replacement for switch statements — far more flexible, and just as safe as if when used as an expression.
3. Loops and Rangesfor, while, and the range expressions (1..10, downTo, step) that make Kotlin's loops read like plain English.

Functions

1. Functions, Default and Named ArgumentsDeclaring functions in Kotlin, and the default/named argument features that eliminate most overload boilerplate.
2. Single-Expression FunctionsThe = shorthand for functions whose body is one expression, and how it works with type inference.
3. Lambdas and Higher-Order FunctionsPassing behavior as a value — anonymous functions and the functions that accept them as parameters.

Collections

1. Lists, Sets, and MapsKotlin's three core collection types, and the mutable/read-only distinction that runs through all of them.
2. Functional Collection Operationsmap, filter, reduce, and the other higher-order functions that replace hand-written loops for transforming collections.

Classes & Object-Oriented Kotlin

1. Classes and ObjectsDeclaring classes, constructors, and properties — and how Kotlin collapses fields, getters, and setters into one concept.
2. Data ClassesThe data class declaration that generates equals, hashCode, toString, and copy for classes that primarily hold values.
3. Inheritance and InterfacesWhy Kotlin classes are closed to inheritance by default, and how open, override, and interfaces work together.
4. Extension FunctionsAdding new functions to existing classes — including ones you don't own the source of — without inheritance.
5. Sealed ClassesRestricting a type to a known, closed set of subclasses so the compiler can verify every case is handled.

Concurrency & Beyond

1. Coroutines Basicssuspend functions, launch, and async — Kotlin's lightweight approach to writing asynchronous code that reads like sequential code.
2. Where to Go Next — Jetpack ComposeA brief look at Jetpack Compose, Android's modern declarative UI framework built entirely on Kotlin.