In Kotlin, the size property determines the number of elements within a collection. It is not only applicable to lists but also to other collections that we’ll be working with in the coming lessons.

Similarly to the length property for Strings, size counts the number of elements in a collection and returns an Integer value.

Take a look at the following list of major European rivers:

val majorRivers = listOf("Volga", "Danube", "Loire", "Rhine", "Elbe") 

We can append size to majorRivers and retrieve the number of elements in the list:

println(majorRivers.size) // Prints: 5  

Additionally, this code can be used to construct an informative String about our list:

println("There are ${majorRivers.size} major rivers in Europe.") 
// Prints: There are 5 major rivers in Europe.  

Furthermore, size can be used along with an element’s index to retrieve the last element of a collection:

println(majorRivers[majorRivers.size - 1]) // Prints: Elbe

• Within the brackets, majorRivers.size equates to 5. Subtracting 1 from this value results in 4 which becomes the final numerical index within the brackets.
• majorRivers[4] returns the 4th and last element in the list, "Elbe".

This strategy is most commonly used when iterating over a collection or simply grabbing the last element of a list when we don’t know how many list elements there are in total. We’ll learn more about how to iterate over a collection later in the course.