Kotlin Data Types

Overview of Data Types

Kotlin has a rich type system and is statically typed. Basic types include:

Int, Long, Short, Byte
Float, Double
Char, Boolean, String

val count: Int = 42
val pi: Double = 3.14
val grade: Char = 'A'
val isPassed: Boolean = true
val name: String = "Kotlin"

Type Inference

Kotlin automatically infers types when possible:

val score = 99          // Int
val version = 1.8       // Double
val language = "Kotlin" // String

Use explicit typing when needed for clarity or external APIs.

Nullable Types

Kotlin’s type system distinguishes between nullable and non-null types. Use ? to declare a variable that can hold null.

var city: String? = "Toronto"
city = null // OK

var country: String = "Canada"
country = null // ❌ Compile-time error

Safe Access and Null Handling

Kotlin provides several powerful operators to handle null values safely and concisely. These include the safe call operator ?., the Elvis operator ?:, and the non-null assertion operator !!.

?. — Safe Call: Accesses a property or method only if the variable is not null. If it is null, the whole expression evaluates to null (instead of throwing an exception).
?: — Elvis Operator: Provides a default value if the expression on the left is null.
!! — Non-null Assertion: Forces the variable to be treated as non-null. Will throw a NullPointerException if the variable is actually null.

Example:

val city: String? = null

println(city?.length)         // Safe call: prints null instead of crashing
println(city ?: "Unknown")    // Elvis operator: prints "Unknown"
println(city!!.length)        // ❌ Throws NullPointerException (do not use unless you're 100% sure city is not null)

Type Conversion

Kotlin does not allow implicit conversions between number types:

val a: Int = 10
val b: Long = a.toLong()
val f: Float = b.toFloat()

Use toInt(), toDouble(), etc. for explicit conversions.

String Templates

Kotlin supports string interpolation using $ syntax:

Output:

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