Kotlin Cookbook

Chapter 5. Collections

As in Java, Kotlin uses typed collections to hold multiple objects. Unlike Java, Kotlin adds many interesting methods directly to the collection classes, rather than going through a stream intermediary.

Recipes in this chapter discuss ways to process both arrays and collections, ranging from sorting and searching, to providing read-only views, to accessing windows of data, and more.

5.1 Working with Arrays

Problem

You want to create and populate arrays in Kotlin.

Solution

Use the arrayOf function to create them, and the properties and methods inside the Array class to work with the contained values.

Discussion

Virtually every programming language has arrays, and Kotlin is no exception. This book focuses on Kotlin running on the JVM, and in Java arrays are handled a bit differently than they are in Kotlin. In Java you instantiate an array using the keyword new and dimensioning the array, as in Example 5-1.

Example 5-1. Instantiating an array in Java

String[] strings = new String[4];
strings[0] = "an";
strings[1] = "array";
strings[2] = "of";
strings[3] = "strings";

// or, more easily,
strings = "an array of strings".split(" ");

Kotlin provides a simple factory method called arrayOf for creating arrays, and while it uses the same syntax for accessing elements, in Kotlin Array is a class. Example 5-2 shows how the factory method works.

Example 5-2. Using the arrayOf factory method

val strings = arrayOf("this", "is", "an", "array", "of", "strings" ...