Kotlin Classes
Creating blueprints for objects
🏗️ What are Classes?
Classes in Kotlin are blueprints for creating objects. They define properties (data) and functions (behavior) that objects will have. Think of a class as a template for making similar things.
// Simple class definition
class Car {
var brand = "Unknown"
var model = "Unknown"
fun start() {
println("$brand $model is starting...")
}
}
Usage:
val myCar = Car()
myCar.brand = "Toyota"
myCar.start() // Toyota Unknown is starting...
Key Class Concepts
Properties
Variables that store data
var name: String = "John"Functions
Actions the class can perform
fun speak() { println("Hello") }Objects
Instances created from classes
val person = Person()Encapsulation
Controlling access to data
private var age: Int = 0🔹 Basic Class Structure
Here's how to create a simple class with properties and functions:
class Person {
// Properties (variables)
var name: String = ""
var age: Int = 0
// Functions (methods)
fun introduce() {
println("Hi, I'm $name and I'm $age years old")
}
fun haveBirthday() {
age++
println("Happy birthday! Now I'm $age")
}
}
fun main() {
val person = Person()
person.name = "Alice"
person.age = 25
person.introduce()
person.haveBirthday()
}Output:
Hi, I'm Alice and I'm 25 years old
Happy birthday! Now I'm 26
🔹 Class with Primary Constructor
You can initialize properties directly when creating an object:
class Dog(var name: String, var breed: String) {
fun bark() {
println("$name the $breed says: Woof!")
}
fun fetch() {
println("$name is fetching the ball!")
}
}
fun main() {
val myDog = Dog("Buddy", "Golden Retriever")
myDog.bark()
myDog.fetch()
}Output:
Buddy the Golden Retriever says: Woof!
Buddy is fetching the ball!
🔹 Private Properties
Use private to hide data and provide controlled access:
class BankAccount(private var balance: Double) {
fun deposit(amount: Double) {
if (amount > 0) {
balance += amount
println("Deposited $amount. New balance: $balance")
}
}
fun withdraw(amount: Double) {
if (amount > 0 && amount <= balance) {
balance -= amount
println("Withdrew $amount. New balance: $balance")
} else {
println("Insufficient funds!")
}
}
fun getBalance(): Double {
return balance
}
}
fun main() {
val account = BankAccount(100.0)
account.deposit(50.0)
account.withdraw(30.0)
println("Current balance: ${account.getBalance()}")
}Output:
Deposited 50.0. New balance: 150.0
Withdrew 30.0. New balance: 120.0
Current balance: 120.0