Why open keyword is required for inheritance in Kotlin - See It in Action

Why open keyword is required for inheritance

📖 Scenario: Imagine you are creating a simple app with animals. You want to make a base class Animal and then create a specific animal like Dog that inherits from Animal.In Kotlin, classes are final by default, so you need to use the open keyword to allow inheritance.

🎯 Goal: Learn how to use the open keyword in Kotlin to allow a class to be inherited.

📋 What You'll Learn

Create an open class called Animal with a function makeSound() that prints "Some sound"

Create a class called Dog that inherits from Animal

Override the makeSound() function in Dog to print "Bark"

Create an instance of Dog and call makeSound() to see the output

💡 Why This Matters

🌍 Real World

Understanding the <code>open</code> keyword is important when designing apps that use inheritance, like games with different characters or apps with reusable components.

💼 Career

Many Kotlin jobs require knowledge of class inheritance and how to control it with <code>open</code> and <code>final</code> keywords to write safe and maintainable code.

1

Create an open class Animal

Create an open class called Animal with a function makeSound() that prints "Some sound".

Kotlin

# Your code here

Need a hint?

Remember to use open before the class and the function to allow inheritance and overriding.

2

Create a class Dog that inherits from Animal

Create a class called Dog that inherits from Animal.

Kotlin

open class Animal {
    open fun makeSound() {
        println("Some sound")
    }
}

# Your code here

Need a hint?

Use class Dog : Animal() to inherit from Animal.

3

Override makeSound() in Dog

Override the makeSound() function in Dog to print "Bark".

Kotlin

open class Animal {
    open fun makeSound() {
        println("Some sound")
    }
}

class Dog : Animal() {
    # Your code here
}

Need a hint?

Use override fun makeSound() inside Dog to change the behavior.

4

Create Dog instance and call makeSound()

Create an instance of Dog called dog and call dog.makeSound() to print the sound.

Kotlin

open class Animal {
    open fun makeSound() {
        println("Some sound")
    }
}

class Dog : Animal() {
    override fun makeSound() {
        println("Bark")
    }
}

# Your code here

Need a hint?

Create val dog = Dog() and then call dog.makeSound() inside main().