Kotlin Collections

Question 1

What is collection?

Answer 1

Collection usually contains a number of objects (this number may also be zero) of the same type. Objects in a collection are called elements or items. For example, all the students in a department form a collection that can be used to calculate their average age.

Question 2

Collection types relevant for Kotlin and their description

Answer 2

List is an ordered collection with access to elements by indices – integer numbers that reflect their position. Elements can occur more than once in a list. An example of a list is a sentence: it’s a group of words, their order is important, and they can repeat.

• Set is a collection of unique elements. It reflects the mathematical abstraction of set: a group of objects without repetitions. Generally, the order of set elements has no significance. For example, an alphabet is a set of letters.
• Map (or dictionary) is a set of key-value pairs. Keys are unique, and each of them maps to exactly one value. The values can be duplicates. Maps are useful for storing logical connections between objects, for example, an employee’s ID and their position.