Kotlin Variables and Constants

Kotlin Variables and Constants

Variables and constants are fundamental building blocks in any programming language. In Kotlin, we have two main ways to declare them: val for constants and var for variables. Let’s explore how they work and when to use each.

Understanding val and var

val (Immutable)

val name = "John"  // Type inference
val age: Int = 25  // Explicit type
val PI = 3.14159   // Constant value

var (Mutable)

var count = 0
var message: String = "Hello"
var temperature = 36.5

Type Inference

Kotlin is smart enough to infer types in most cases:

val text = "Hello"     // String
val number = 42        // Int
val decimal = 3.14     // Double
val isActive = true    // Boolean
val list = listOf(1, 2, 3)  // List<Int>

Basic Types

Numbers

val intNumber: Int = 42
val longNumber: Long = 42L
val floatNumber: Float = 42.0f
val doubleNumber: Double = 42.0

Characters and Strings

val char: Char = 'A'
val string: String = "Hello"
val multiLineString = """
    This is a
    multi-line
    string
""".trimIndent()

Booleans

val isTrue: Boolean = true
val isFalse: Boolean = false

Variable Scope

Local Variables

fun example() {
    val localVar = "I'm local"
    println(localVar)
}

Class Properties

class Person {
    val name: String = "John"  // Property
    var age: Int = 25          // Mutable property
}

Best Practices

1. Prefer val over var

   • Use val by default
   • Only use var when the value needs to change

2. Use meaningful names

   // Good
   val userAge = 25
   val maximumCount = 100
   
   // Avoid
   val a = 25
   val x = 100
   

3. Constants

   const val MAX_SIZE = 100
   const val API_URL = "https://api.example.com"
   

Type Safety

Kotlin is statically typed, which means:

• Types are checked at compile time
• Type mismatches are caught early
• Better IDE support and code completion

var number: Int = 42
number = "Hello"  // Error: Type mismatch

Null Safety

Variables can be nullable or non-null:

var nonNullName: String = "John"  // Can't be null
var nullableName: String? = null  // Can be null

Conclusion

Understanding variables and constants in Kotlin is crucial for writing clean and maintainable code. Remember:

• Use val for immutable values
• Use var only when necessary
• Leverage type inference
• Follow naming conventions
• Be mindful of null safety

Stay tuned for our next post where we’ll explore control flow in Kotlin!