Kotlin Collections
Working with lists, arrays, and data structures
📚 What are Kotlin Collections?
Collections are data structures that hold multiple elements. Kotlin provides powerful collection types like lists, sets, and maps with rich functionality for filtering, mapping, and transforming data efficiently and safely.
// Creating different collections
val numbers = listOf(1, 2, 3, 4, 5)
val mutableList = mutableListOf("A", "B", "C")
println("Numbers: $numbers")
println("Letters: $mutableList")
Output:
Numbers: [1, 2, 3, 4, 5]
Letters: [A, B, C]
Collection Types
Lists
Ordered collections with duplicates
val list = listOf(1, 2, 3, 2)Arrays
Fixed-size collections
val array = arrayOf(1, 2, 3)Mutable Collections
Collections you can modify
val mutable = mutableListOf(1, 2)Operations
Filter, map, and transform data
list.filter { it > 2 }🔹 Creating Lists
Different ways to create and work with lists:
// Immutable list
val fruits = listOf("Apple", "Banana", "Orange")
// Mutable list
val colors = mutableListOf("Red", "Green", "Blue")
colors.add("Yellow")
// Empty lists
val emptyList = emptyList<String>()
val emptyMutable = mutableListOf<Int>()
println("Fruits: $fruits")
println("Colors: $colors")
println("First fruit: ${fruits[0]}")
println("List size: ${fruits.size}")Output:
Fruits: [Apple, Banana, Orange]
Colors: [Red, Green, Blue, Yellow]
First fruit: Apple
List size: 3
🔹 Collection Operations
Transform and filter collections with powerful operations:
val numbers = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
// Filter even numbers
val evenNumbers = numbers.filter { it % 2 == 0 }
// Map to squares
val squares = numbers.map { it * it }
// Find first number greater than 5
val firstBig = numbers.first { it > 5 }
// Check if any number is greater than 8
val hasLarge = numbers.any { it > 8 }
println("Even numbers: $evenNumbers")
println("Squares: $squares")
println("First > 5: $firstBig")
println("Has > 8: $hasLarge")Output:
Even numbers: [2, 4, 6, 8, 10]
Squares: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
First > 5: 6
Has > 8: true
🔹 Working with Arrays
Arrays are fixed-size collections with specific types:
// Different array types
val intArray = arrayOf(1, 2, 3, 4, 5)
val stringArray = arrayOf("Hello", "World")
val boolArray = booleanArrayOf(true, false, true)
// Array operations
val doubled = intArray.map { it * 2 }
val joined = stringArray.joinToString(" ")
// Convert between arrays and lists
val arrayToList = intArray.toList()
val listToArray = listOf(6, 7, 8).toTypedArray()
println("Int array: ${intArray.contentToString()}")
println("Doubled: $doubled")
println("Joined: $joined")
println("Array to list: $arrayToList")Output:
Int array: [1, 2, 3, 4, 5]
Doubled: [2, 4, 6, 8, 10]
Joined: Hello World
Array to list: [1, 2, 3, 4, 5]