Lectures

Autocomplete, templates, and refactoring. IntelliJ IDEA is Kotlin’s native home. Learn how to write code at the speed of thought using Tab, Live Templates, Postfix Completion, and formatting hotkeys.

We break down how to turn input in a console program into neat utilities: move the prompt ( prompt) into a parameter, read a line via readln(), safely parse values via toIntOrNull()/ toDoubleOrNull(), and return types like Int?/ Double?. At the script level, we learn to work with nullable values using the Elvis operator ?: and early exit with run { ...; return }, keeping the “happy path” flat and readable.

We break down how, in Kotlin, to separate input from data conversion: we build “silent” functions of the form String → T ?, normalize strings with trim() and lowercase(), write parsers parseIntOrNull, parseDoubleOrNull, parseYesNoOrNull, and then neatly “glue” them to console input. At the end, there’s a mini questionnaire scenario and a list of common mistakes.

We break down the “validation as a separate layer” approach: how parsing ( String → T?) differs from rule-checking ( T → T?), why it’s convenient to signal an error via null, how to check ranges with in and min..max, and how to validate strings as “not empty” after trim(). At the end — the composition readln() → toIntOrNull() → validator, and a list of typical mistakes.

We break down the fail-fast style in Kotlin: how to separate expected data errors (return null and handle it in the scenario) from programmer errors (stop via require()/ check()). Using practical input and validation utilities, we will show the difference between IllegalArgumentException and IllegalStateException, learn to write good messages, and rewrite the “pyramid” of nested if into linear code with guard clauses (early return).

We break down how to assemble a small and honest set of input functions for Kotlin console programs: we extract repeated steps ( prompt, trim(), safe parsing via toIntOrNull()/ toDoubleOrNull(), range validation), introduce naming conventions ( read…, parse…, validate…, the OrNull suffix), show “building-block” composition, and write a readable main() as a script without copy-paste.

How to find a bug without losing your mind. Learn to use the Debugger: breakpoints, step-by-step execution, inspecting variables, and evaluating expressions on the fly.