Lectures

Let’s break down how the for loop works in Kotlin “under the hood”: why it relies on the Iterable<T> contract, how Iterator<T> is created and used, what the methods iterator(), hasNext(), and next() do, and which mistakes most often happen when manually iterating collections. At the end, there’s a mini practice task: printing tasks in SimplePlanner.

We break down List iteration styles in Kotlin: when a for loop over values is enough, what the difference is between size and lastIndex, how to safely iterate by indices via indices, and how to print “number + value” using withIndex(). We’ll also discuss boundaries, empty lists, a mini example for a Task CLI, and common mistakes that lead to IndexOutOfBoundsException.

We’ll break down why Map cannot be iterated “by indexes”, how to work with the views keys/ values/ entries, what Map.Entry is and how it differs from Pair. We’ll learn how to choose an iteration style (keys, values, or pairs), use destructuring ( k , v ) in a loop, and also reinforce everything with a practical example of an expense-category report and analyze common mistakes.

We break down why removing elements “on the fly” often leads to ConcurrentModificationException or silent logic bugs, and learn how to choose the right strategy in Kotlin/JVM: removal via MutableIterator. remove(), iterating a list by indices from right to left with removeAt, as well as safely cleaning a MutableMap via an iterator over entries.

We break down how to organize a “command menu” in a Kotlin console application: normalize a line with trim(), parse the command and argument into a Pair, route actions via when, and safely update a MutableList<String>. We also compare removeAt(index) and remove(value), show correct multiple deletion via an iterator, and highlight common mistakes (index vs number, bounds checks, deleting inside for).