Abstract Classes क्या हैं

abstract class Shape {
    abstract fun area(): Double
}

// Define a class `Circle`
class Circle(val radius: Double) : Shape() {
    override fun area(): Double = Math.PI * radius * radius
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `circle`, set to `Circle(3.0)`
    val circle = Circle(3.0)
    // Print "Area: ${circle.area()}" to the console, with a trailing newline
    println("Area: ${circle.area()}")
}

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abstract class Employee(val name: String) {
    abstract fun monthlySalary(): Double
}

// Define a class `Manager`
class Manager(name: String, val baseSalary: Double) : Employee(name) {
    override fun monthlySalary(): Double = baseSalary * 1.2
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `manager`, set to `Manager("Ana", 5000.0)`
    val manager = Manager("Ana", 5000.0)
    // Print "${manager.name}'s salary: ${manager.monthlySalary()}" to the console, with a trailing newline
    println("${manager.name}'s salary: ${manager.monthlySalary()}")
}

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abstract class Shape {
    abstract fun area(): Double

    // Define the function `describe` with no parameters and returning a String
    fun describe(): String = "This shape has area ${area()}"
}

// Define a class `Square`
class Square(val side: Double) : Shape() {
    override fun area(): Double = side * side
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `square`, set to `Square(5.0)`
    val square = Square(5.0)
    // Print `square.describe()` to the console, with a trailing newline
    println(square.describe())
}

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abstract class PaymentMethod {
    abstract fun pay(amount: Double): String
}

// Define a class `CreditCard`
class CreditCard : PaymentMethod() {
    override fun pay(amount: Double): String = "Paid $$amount with credit card"
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `payment` (a `PaymentMethod`), set to `CreditCard()`
    val payment: PaymentMethod = CreditCard()
    // Print `payment.pay(49.99)` to the console, with a trailing newline
    println(payment.pay(49.99))
}

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