Classes and Objects

1. What is a class in Kotlin?

A class is a blueprint for creating objects. It defines properties and behaviors that the objects created from the class will have.

2. How do you define a class in Kotlin?

Use the class keyword followed by the class name.

3. What is an object in Kotlin?

An object is an instance of a class. It represents a real-world entity and has its own unique state.

4. How do you create an instance of a class in Kotlin?

Use the val or var keyword followed by the instance name and the class constructor.

5. Explain the difference between a class and an object.

A class is a blueprint or template for creating objects, while an object is an instance of a class.

6. What are properties in Kotlin classes?

Properties are the characteristics or attributes of a class. They define the state of an object.

7. What are methods in Kotlin classes?

Methods are functions defined within a class. They represent the behavior of the objects created from the class.

8. How is inheritance implemented in Kotlin?

Use the : symbol followed by the name of the superclass after the subclass declaration.

9. Explain the concept of visibility modifiers in Kotlin.

Visibility modifiers (private, protected, internal, public) control the visibility of classes, properties, and methods.

10. What is the primary constructor in Kotlin?

The primary constructor is declared in the class header. It defines the properties of the class.

11. How do you create secondary constructors in Kotlin?

Use the constructor keyword along with this to define secondary constructors.

12. What is a data class in Kotlin?

A data class is a class specifically designed for holding data. It automatically generates equals(), hashCode(), toString(), and copy() methods.

13. Explain the init block in Kotlin.

The init block is executed when an instance of the class is created. It is used for additional initialization.

14. What is the purpose of the companion object in Kotlin?

The companion object is used to create static members and methods in a class.

15. Explain the difference between val and var in the context of class properties.

val is used for read-only (immutable) properties, and var is used for mutable properties.

16. How does Kotlin handle method overloading?

Method overloading is supported in Kotlin by defining multiple methods with the same name but different parameter lists.

17. What is an abstract class in Kotlin?

An abstract class cannot be instantiated and may contain abstract (unimplemented) methods. Subclasses must provide implementations.

18. How is a sealed class different from a regular class in Kotlin?

A sealed class is a limited hierarchy where all subclasses are known. It is often used in when expressions to ensure exhaustive checks.

19. What is the purpose of the by lazy delegate in Kotlin?

The by lazy delegate is used for lazy initialization of properties. It computes the value only when the property is accessed for the first time.

20. Explain the object keyword in Kotlin.

The object keyword is used to define a singleton object – a class that can have only one instance.