List of lectures for the course Kotlin, 47 quest level on JavaRush

Introduction to serialization
Kotlin SELF
47 level,0 lecture
We break down what serialization and deserialization are in Kotlin/JVM: why objects like List<Expense> need a portable form (string/bytes), why you can’t treat toString() as a “storage format”, why hand-assembling JSON without escaping is dangerous, and why any storage schema is a data contract (fields, types, version compatibility). At the end— a mini sketch of a file structure and common mistakes when designing persistence.
Open
JSON Structure and Its Relationship to Kotlin Types
Kotlin SELF
47 level,1 lecture
We break down the JSON “alphabet”: an object {...}, an array [...], primitives, and null, and map them to Kotlin types: data class, Map, List, String, Int/ Long/ Double, nullable types T?. We learn to “read JSON with our eyes,” understand nesting, and catch typical mistakes early (quotes around keys, trailing commas, mixing up strings and numbers, null vs "null").
Open
Adding kotlinx.serialization and the @Serializable annotation
Kotlin SELF
47 level,2 lecture
We break down why serialization is needed in Kotlin projects, how kotlinx.serialization works (compiler plugin + runtime), how to correctly add kotlin("plugin.serialization") and the dependency on the JSON module, and how to apply the @Serializable annotation to models ( Expense, AppState). At the end, there is a quick test via serializer() and a walkthrough of typical mistakes.
Open
Basic encode/ decode pipeline + storing JSON in a file
Kotlin SELF
47 level,3 lecture
We walk through an honest end-to-end data persistence chain for a console Kotlin project: how to serialize an object and a list to JSON via Json.encodeToString, write the JSON string to a file ( writeText), then read it back ( readText) and restore the data via Json.decodeFromString. We also discuss error diagnostics (I/O vs JSON parsing) and common pitfalls like toString(), a missing directory, and confusion between {} and [].
Open
Configuring Json { ... }: readability, compatibility, strictness
Kotlin SELF
47 level,4 lecture
We break down kotlinx.serialization.json.Json settings as part of the data storage “contract”: how prettyPrint helps with readability and diffs, how encodeDefaults affects file “self-sufficiency”, why explicitNulls changes the meaning of “field is missing” vs “field = null”, and how to achieve compatibility via ignoreUnknownKeys and careful importing with isLenient. At the end: a practical template for a single appJson for the whole application and a walkthrough of common mistakes.
Open