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In Kotlin, classes and members are final by default, so you must explicitly mark them as open if you want them to be inherited or overridden. Basic class inheritance open class Animal { open fun makeSound() { println("Some sound") } } class Dog : Animal() { override fun makeSound() { println("Bark") } } Usage: fun […]
In Kotlin, an init block runs setup logic when a class instance is created. It is commonly used to validate constructor arguments, initialize derived properties, or perform other construction-time setup. class User(val name: String, val age: Int) { init { require(name.isNotBlank()) { "Name must not be blank" } require(age >= 0) { "Age must be […]
In Kotlin, you usually don’t manually override toString(), equals(), and hashCode() if your class is just a value/data holder. Use a data class instead. data class User( val id: Int, val name: String ) Kotlin automatically generates: toString() equals() hashCode() copy() componentN() Example: val a = User(1, "Alice") val b = User(1, "Alice") println(a) // […]
In Kotlin, data classes are designed to store structured data with minimal boilerplate. A data class automatically provides useful functions such as: toString() equals() hashCode() copy() component functions for destructuring, like component1(), component2() Basic example data class User( val id: Int, val name: String, val email: String ) You can create and use it like […]
In Kotlin classes, val and var are used to declare properties. val means read-only after initialization var means mutable / can be reassigned Basic example class User { val id: Int = 1 var name: String = "Alice" } Usage: fun main() { val user = User() println(user.id) // 1 println(user.name) // Alice user.name = […]
In Kotlin, you usually define constructors and initialize properties directly in the class header using a primary constructor. 1. Primary constructor The most common style is: class Person(val name: String, var age: Int) This defines: a class named Person a read-only property name a mutable property age a constructor that requires both values Usage: fun […]
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