Kotlin Flashcards

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Kotlin is a modern and versatile programming language developed by JetBrains, widely used especially in Android application development. Introduced in 2011 and reaching stability in 2016, Kotlin is known for its clarity, safety, and interoperability with Java. The language offers numerous benefits, including null safety, the ability to program both functionally and object-oriented, and easy integration with existing Java projects. With an active community and continuous development, Kotlin has become a popular choice in modern software development.

Our flashcard app contains 115 carefully selected Kotlin interview questions, complete with comprehensive answers, to effectively prepare you for any interview requiring Kotlin knowledge. IT Flashcards is not just a tool for job seekers – it’s an excellent way to strengthen and test your knowledge, regardless of your current career plans. Regular use of the app will help you stay updated with the latest trends in Kotlin and maintain your skills in mobile app development at a high level.

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What is Kotlin?

Kotlin is a modern, statically-typed programming language developed by JetBrains, known for producing popular development environments such as IntelliJ IDEA, PyCharm, and WebStorm.

The language was designed with mobile application development for the Android platform in mind, but it can also be used for software development on various other platforms, such as iOS, Front-end web, JVM, Linux/Windows/Mac.

Kotlin is an open-source language, supported by Google. In 2019, it became the preferred language for developing new applications on the Android platform.

Its main features are:
1. **Safety**: Kotlin has features that automatically eliminate NullPointerException errors.
2. **Interoperability with Java**: Kotlin is fully interoperable with Java, meaning you can use Java code in Kotlin and vice versa.
3. **Shorter and more readable code** compared to Java: Kotlin is more expressive thanks to features such as default arguments, destructuring, immutable data types, etc.

Readable Kotlin code reduces application maintenance costs and also makes it easier for other developers to understand the code.

What are coroutines in Kotlin?

Coroutines in Kotlin are a language feature that enables the creation of non-blocking and asynchronous operations. With the help of coroutines, you can express instances of suspended computations that can be deferred and then resumed at a later time.

Coroutines are very lightweight and can be used to create a larger number of operations within a single thread. For example, thousands of coroutines can operate efficiently within a single thread, whereas creating a separate thread for each operation would be inefficient.

Coroutines are run within a context that is a set of operational elements. The `scope` of the coroutines defines how a coroutine is related to other coroutines and determines the lifecycle rules that apply to it.

Example coroutine definition:

suspend fun firstCoroutine() {
    delay(1000L)
    println("Hello from coroutine")
}

Using the `suspend` modifier means that the function can only run in the context of a coroutine. The primary goal of coroutines is to enable writing asynchronous code in a sequential manner without requiring complicated handling mechanisms. They improve code readability and reduce the likelihood of errors.

What is the difference between val and var in Kotlin?

In Kotlin, val and var are used for variable declarations, but they differ in terms of mutability.

A variable declared with val is immutable, meaning that once its value is initialized, it cannot be changed. This is equivalent to a final variable in Java.

A variable declared with var is mutable, meaning that its value can be changed.

Here is a sample code demonstrating the difference between val and var:

val name = "John" // value cannot be changed
var age = 25 // value can be changed

age = 26 // OK
name = "Tom" // ERROR: Val cannot be reassigned

When you create a variable using val, you assign its value for the first time and cannot change it afterwards. When you create a variable using var, you can change its value multiple times.

What is a data class in Kotlin?

Data Class in Kotlin is a special type of class used to create typical objects of a given class. These are classes that essentially violate the single responsibility principle and contain only data in the form of fields. They are mainly used for storing data.

Data Class in Kotlin generates standard methods like equals(), hashCode(), and toString() automatically. Moreover, the Kotlin compiler creates standard copy and component functions that significantly ease the work.

To define a Data Class, simply add the keyword `data` before the class declaration.

Here is an example of using a Data Class in Kotlin:

data class User(val name: String, val age: Int)

In the example above, `User` is a data class with two fields, `name` and `age`. By being a data class, `User` automatically has generated methods like equals(), hashCode(), toString(), copy(), and component functions.

Using data classes significantly simplifies the code and makes it more readable, while also protecting against errors related to manually implementing the aforementioned methods.