Kotlin Built-in Functions
Essential functions available in Kotlin standard library
🛠️ What are Built-in Functions?
Kotlin provides many built-in functions in its standard library for common operations like printing, string manipulation, collections processing, and type checking. These functions make coding more efficient and readable.
// Common built-in functions
println("Hello, World!") // Print with newline
val numbers = listOf(1, 2, 3, 4, 5)
val doubled = numbers.map { it * 2 } // Transform collection
Function Categories
I/O Functions
Input and output operations
println("Hello")
print("No newline")
readLine()Collection Functions
Process lists, sets, and maps
map(), filter(), reduce()
forEach(), any(), all()String Functions
Manipulate and check strings
length, isEmpty()
contains(), startsWith()Type Functions
Check and convert types
is, as, as?
toString(), toInt()🔹 I/O Functions
Functions for input and output operations:
fun demonstrateIO() {
// Output functions
println("This prints with a newline")
print("This prints without newline ")
print("- continues on same line\n")
// Formatted output
val name = "Alice"
val age = 25
println("Name: $name, Age: $age")
printf("Formatted: Name is %s and age is %d\n", name, age)
// Input function (commented for demo)
// print("Enter your name: ")
// val userInput = readLine() ?: "Unknown"
// println("Hello, $userInput!")
// Error output
System.err.println("This is an error message")
}Output:
This prints with a newline This prints without newline - continues on same line Name: Alice, Age: 25 Formatted: Name is Alice and age is 25
🔹 Collection Functions
Powerful functions for working with collections:
fun demonstrateCollections() {
val numbers = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
// Transform collections
val doubled = numbers.map { it * 2 }
println("Doubled: $doubled")
// Filter collections
val evenNumbers = numbers.filter { it % 2 == 0 }
println("Even numbers: $evenNumbers")
// Reduce/fold operations
val sum = numbers.reduce { acc, n -> acc + n }
val product = numbers.fold(1) { acc, n -> acc * n }
println("Sum: $sum, Product: $product")
// Check conditions
val hasEven = numbers.any { it % 2 == 0 }
val allPositive = numbers.all { it > 0 }
println("Has even: $hasEven, All positive: $allPositive")
// Find elements
val firstEven = numbers.first { it % 2 == 0 }
val lastOdd = numbers.last { it % 2 == 1 }
println("First even: $firstEven, Last odd: $lastOdd")
// Group and partition
val grouped = numbers.groupBy { it % 3 }
val (evens, odds) = numbers.partition { it % 2 == 0 }
println("Grouped by mod 3: $grouped")
println("Evens: $evens, Odds: $odds")
}Output:
Doubled: [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
Even numbers: [2, 4, 6, 8, 10]
Sum: 55, Product: 3628800
Has even: true, All positive: true
First even: 2, Last odd: 9
Grouped by mod 3: {1=[1, 4, 7, 10], 2=[2, 5, 8], 0=[3, 6, 9]}
Evens: [2, 4, 6, 8, 10], Odds: [1, 3, 5, 7, 9]
🔹 String Functions
Built-in functions for string manipulation:
fun demonstrateStrings() {
val text = " Hello, Kotlin World! "
// Basic properties
println("Length: ${text.length}")
println("Is empty: ${text.isEmpty()}")
println("Is blank: ${text.isBlank()}")
// Trimming and case
val cleaned = text.trim()
println("Trimmed: '$cleaned'")
println("Uppercase: ${cleaned.uppercase()}")
println("Lowercase: ${cleaned.lowercase()}")
// Checking content
println("Contains 'Kotlin': ${cleaned.contains("Kotlin")}")
println("Starts with 'Hello': ${cleaned.startsWith("Hello")}")
println("Ends with '!': ${cleaned.endsWith("!")}")
// Splitting and joining
val words = cleaned.split(" ")
println("Words: $words")
val rejoined = words.joinToString(" - ")
println("Rejoined: $rejoined")
// Replacing
val replaced = cleaned.replace("Kotlin", "Programming")
println("Replaced: $replaced")
// Substring operations
val substring = cleaned.substring(7, 13) // "Kotlin"
println("Substring: $substring")
// String templates and formatting
val name = "Alice"
val age = 30
val formatted = "Name: $name, Age: $age"
println("Formatted: $formatted")
}Output:
Length: 23 Is empty: false Is blank: false Trimmed: 'Hello, Kotlin World!' Uppercase: HELLO, KOTLIN WORLD! Lowercase: hello, kotlin world! Contains 'Kotlin': true Starts with 'Hello': true Ends with '!': true Words: [Hello,, Kotlin, World!] Rejoined: Hello, - Kotlin - World! Replaced: Hello, Programming World! Substring: Kotlin Formatted: Name: Alice, Age: 30
🔹 Type Checking and Conversion
Functions for working with types and conversions:
fun demonstrateTypes() {
val value: Any = "123"
// Type checking
if (value is String) {
println("Value is a String: $value")
println("Length: ${value.length}") // Smart cast
}
// Safe casting
val stringValue = value as? String
println("Safe cast result: $stringValue")
val intValue = value as? Int
println("Safe cast to Int: $intValue") // null
// Type conversions
val numberString = "42"
val number = numberString.toInt()
val double = numberString.toDouble()
val boolean = "true".toBoolean()
println("String to Int: $number")
println("String to Double: $double")
println("String to Boolean: $boolean")
// Converting back to strings
println("Int to String: ${number.toString()}")
println("Double to String: ${double.toString()}")
// Null safety functions
val nullableString: String? = null
val length = nullableString?.length ?: 0
println("Safe length: $length")
// let, run, apply, also functions
val result = "Hello".let { str ->
str.uppercase().reversed()
}
println("Let result: $result")
val person = Person("John", 25).apply {
println("Created person: $name, age $age")
}
}
data class Person(val name: String, val age: Int)Output:
Value is a String: 123 Length: 3 Safe cast result: 123 Safe cast to Int: null String to Int: 42 String to Double: 42.0 String to Boolean: true Int to String: 42 Double to String: 42.0 Safe length: 0 Let result: OLLEH Created person: John, age 25
🔹 Math and Utility Functions
Mathematical and utility functions:
import kotlin.math.*
import kotlin.random.Random
fun demonstrateMathAndUtils() {
// Math functions
val x = 16.0
println("Square root of $x: ${sqrt(x)}")
println("Power 2^3: ${2.0.pow(3.0)}")
println("Absolute value of -5: ${abs(-5)}")
println("Max of 10 and 20: ${max(10, 20)}")
println("Min of 10 and 20: ${min(10, 20)}")
// Rounding
val decimal = 3.7
println("Ceiling of $decimal: ${ceil(decimal)}")
println("Floor of $decimal: ${floor(decimal)}")
println("Round of $decimal: ${round(decimal)}")
// Random numbers
val randomInt = Random.nextInt(1, 11) // 1 to 10
val randomDouble = Random.nextDouble()
println("Random int (1-10): $randomInt")
println("Random double: $randomDouble")
// Range functions
val number = 5
println("5 in range 1..10: ${number in 1..10}")
println("Range 1 to 5: ${(1..5).toList()}")
// Repeat function
repeat(3) { index ->
println("Repeat $index")
}
// Measure time
val timeMillis = measureTimeMillis {
// Simulate some work
Thread.sleep(100)
}
println("Time taken: ${timeMillis}ms")
}Output:
Square root of 16.0: 4.0 Power 2^3: 8.0 Absolute value of -5: 5 Max of 10 and 20: 20 Min of 10 and 20: 10 Ceiling of 3.7: 4.0 Floor of 3.7: 3.0 Round of 3.7: 4.0 Random int (1-10): 7 Random double: 0.8234567 5 in range 1..10: true Range 1 to 5: [1, 2, 3, 4, 5] Repeat 0 Repeat 1 Repeat 2 Time taken: 102ms