Kotlin Interview Questions and Answers for 5 years experience

1. What is Kotlin, and why is it preferred over Java for Android development?

   • Answer: Kotlin is a statically-typed, modern programming language that runs on the Java Virtual Machine (JVM). It's preferred over Java for Android development due to its conciseness (less boilerplate code), null safety features (reducing NullPointerExceptions), improved interoperability with Java, and better support for functional programming paradigms. It offers features like coroutines for asynchronous programming and data classes for simplified data handling, leading to faster development and more maintainable code.

2. Explain Kotlin's null safety features.

   • Answer: Kotlin's null safety is a key feature that helps prevent NullPointerExceptions. It uses the type system to distinguish between nullable and non-nullable types. A nullable type is declared using a `?` (e.g., `String?`), indicating it can hold null values. Accessing a property of a nullable type requires a safe call operator (`?.`) or the Elvis operator (`?:`) to handle potential null values. The `!!` operator forces a non-null value, but should be used cautiously. This system helps developers write more robust code by forcing them to explicitly handle potential null scenarios.

3. What are data classes in Kotlin and how are they useful?

   • Answer: Data classes are a concise way to create classes that primarily hold data. Kotlin automatically generates several methods like `equals()`, `hashCode()`, `toString()`, and `copy()` for data classes, reducing boilerplate code significantly. This simplifies creating classes for representing data structures, making code cleaner and more readable.

4. Explain sealed classes in Kotlin.

   • Answer: Sealed classes are used to represent restricted class hierarchies. A sealed class can have subclasses, but these subclasses must be defined within the same file as the sealed class. This limitation enforces exhaustiveness when using sealed classes in `when` statements, ensuring all possible cases are handled, improving code reliability.

5. What are higher-order functions in Kotlin, and give an example.

   • Answer: Higher-order functions are functions that take other functions as parameters or return functions as results. This enables functional programming paradigms like map, filter, and reduce, which can make code more concise and expressive. Example: `list.map { it * 2 }` applies a lambda function to each element of a list.

6. Explain Kotlin's coroutines and their benefits for asynchronous programming.

   • Answer: Kotlin coroutines provide a lightweight way to write asynchronous code without the complexity of callbacks or threads. They enable writing asynchronous code that looks and behaves like synchronous code, improving readability and maintainability. Coroutines are built on top of Kotlin's suspension function feature, allowing them to suspend execution without blocking the main thread, ensuring responsiveness of the application.

7. How do you handle exceptions in Kotlin?

   • Answer: Kotlin uses `try-catch` blocks to handle exceptions, similar to Java. However, it also encourages the use of null safety to prevent many exceptions related to null values. It supports custom exception classes and allows for more expressive exception handling using features like `finally` blocks.

8. What are extension functions in Kotlin? Give an example.

   • Answer: Extension functions allow you to add new functionality to existing classes without modifying their source code. They are declared using the `.` operator followed by the function name. Example: An extension function to reverse a String: `fun String.reverse(): String { return this.reversed() }`

9. Explain the difference between `val` and `var` in Kotlin.

   • Answer: `val` declares a read-only variable (immutable), similar to a `final` variable in Java. `var` declares a mutable variable, allowing its value to be changed after initialization.

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