Lectures

We break down how an absolute path differs from a relative one, why “file not found” almost always means the wrong working directory, how to see the real address in Kotlin/JVM via absolutePath, and how to build paths neatly without string concatenation (via File(parent, child)). At the end, there’s a short checklist of common mistakes and diagnostics.

We break down why it’s better to store a path not as a String, but as File/ Path objects: how to diagnose relative and absolute paths via path/ absolutePath, what checks to do before I/O ( exists(), isFile, isDirectory), how to prepare directories for writing via parentFile and mkdirs(), and how to assemble a path from parts via File(parent, child) and Path.of(...) without manually concatenating slashes.

We break down three basic ways to read text files in Kotlin/JVM: get the whole file as a String via readText(), load lines into a List<String> via readLines(), or process the file as a stream line by line via forEachLine { ... }. We compare convenience and memory cost, show practical examples (parsing, searching, counting), and point out common mistakes.

We break down writing text files in Kotlin/JVM via java.io.File: how writeText() (full overwrite) differs from appendText() (append to the end), why you need to add the newline "\n" manually, how to create folders in advance via parentFile ?. mkdirs(), and how to neatly organize report and log code in a small console application.

Let’s break down why I/O resources (files, streams, reader/writer) must always be closed, how to guarantee closing via try/ finally, and why the idiomatic way in Kotlin is use { ... }. In practice: reading via bufferedReader(), writing via bufferedWriter(), lazy lines via useLines { ... }, and typical mistakes that lead to “dangling” handles and partially written data.