Kotlin 2.0 Crash Course. Build, test, and secure Android and web applications including Functional patterns, JSON handling, and… (Elara Drevyn)（Z-Library）

【One-Line Pitch】 A hands-on Kotlin 2.0 guide that takes you from installing the toolchain to building, testing, and securing a working Task Tracker app across Android and web targets. Best for developers who already know one language and want a fast, project-driven path into idiomatic Kotlin. 【Book Arc】 - **Opening (~0%–10%)**: Environment setup and first contact — installing JDK, Kotlin 2.0, SDKMAN!, and IntelliJ IDEA on Linux, then running a minimal Task Tracker to close the loop between code and output. - **Early (~10%–30%)**: Language fundamentals through the Task Tracker — variables, data types, collections (lists, sets, maps), control flow with `when`/`while`/`do-while`, and a REPL-style command loop that makes every concept immediately usable. - **Early–Middle (~30%–40%)**: Functions and functional patterns — modular command handlers, higher-order functions, lambdas, inline functions, and a small DSL for batch task operations, all aimed at cutting boilerplate. - **Middle (~40%–50%)**: Object-oriented modeling — data classes, primary and secondary constructors, encapsulation with visibility modifiers, and a service layer that guards internal state behind validated public methods. - **Middle–Late (~50%–70%)**: Collections in depth and data handling — imperative traversal versus declarative pipelines (`filter`, `map`, `groupBy`, `flatMap`), plus JSON serialization with kotlinx.serialization, Moshi, or Jackson, including nested structures and custom serializers. - **Late–Ending (~70%–100%)**: Backend and integration — RESTful API design, CRUD endpoints, database access via Exposed and H2, Ktor server setup with routes and middleware, and systematic testing of each component. (Excerpts do not cover the final chapters in detail.) 【Key Takeaways】 - **Immutability is a design tool, not a restriction** (Early): Favor `val` references and limit `var` to explicit mutation points like an ID counter, making state changes auditable. - **Collections are the backbone of real apps** (Early–Middle): Lists, sets, and maps each solve a distinct problem — ordering, uniqueness, and keyed lookup — and the book shows when to reach for each. - **Functional pipelines replace boilerplate loops** (Middle): Lambdas, higher-order functions, and inline functions let you compose declarative transformations and even build mini-DSLs for domain operations. - **Encapsulation protects invariants** (Middle): Private state plus public service methods ensure every task mutation is validated, persisted, and logged rather than scattered across the codebase. - **Error handling deserves first-class treatment** (Early): Try-catch patterns, safe casts, and centralized logging are presented as a dedicated discipline, not an afterthought. - **JSON handling is a spectrum, not a single tool** (Middle): The book compares kotlinx.serialization, Moshi, and Jackson, and covers nested data classes, dynamic structures, and custom serializers. - **Backend skills complete the picture** (Late): RESTful design, Exposed/H2 persistence, and Ktor routing turn the Task Tracker into a full client-server application. - **Testing is woven throughout** (Late): Each component is tested systematically, reinforcing that verification is part of building, not a separate phase. 【Reading Tips】 - **Deep-read the Early chapters if Kotlin is your first JVM language** — the collection and control-flow material is foundational and the Task Tracker examples build cumulatively. - **Skim the environment setup if you already have a working Kotlin toolchain** — the Linux/JDK/IntelliJ steps are standard and can be revisited only if something breaks. - **Treat the functional programming section as the pivot point** — if lambdas and higher-order functions are new to you, slow down here; everything after (DSLs, pipelines, serialization) depends on this fluency. - **Use the JSON serialization chapter as a reference** — the comparison of kotlinx.serialization, Moshi, and Jackson is worth revisiting when you pick a library for a real project. - **Follow the Task Tracker end-to-end at least once** — the book's value comes from seeing one project evolve from a REPL loop to a tested, database-backed Ktor service. 【Coverage Limits】 This guide is based on stratified excerpts covering roughly the first half of the book in detail, with later chapters (REST, database, Ktor, testing) represented mainly through chapter overviews and summaries. Specific code examples, benchmarks, and final-project details from the later chapters are not fully covered here.