Questions
Kotlin questions
Choose a question page, learn the concept, then test your understanding with a quiz.
Start a New Activity with Intent in Kotlin Android
Learn how to start another Android Activity in Kotlin using Intent, class references, explicit navigation, and correct manifest setup.
Static Extension Methods in Kotlin: What’s Possible and How to Do It
Learn how Kotlin extension functions work, why static extension methods on classes are not supported, and practical alternatives to use instead.
Static Methods and Variables in Kotlin: companion object Guide
Learn how Kotlin companion objects replace Java static methods and variables, with singleton patterns, examples, common mistakes, and a mini project.
String Concatenation in Kotlin: Using +, Templates, and StringBuilder
Learn how to concatenate strings in Kotlin with the + operator, string templates, and StringBuilder, including practical examples and pitfalls.
Swift `if let` Equivalent in Kotlin: Safe Null Handling with `let`, `?.`, and `if`
Learn the Kotlin equivalent of Swift `if let` for nullable values using safe calls, `let`, Elvis, and null checks with clear examples.
Test Expected Exceptions in Kotlin with JUnit
Learn to test expected exceptions in Kotlin with JUnit 4’s expected property and JUnit 5’s assertThrows, plus reliable testing patterns.
Understanding the Kotlin Plugin Version Warning in Gradle for Android and Java Modules
Learn why Android Studio shows a Kotlin plugin version warning in Gradle, even when versions match, and how to handle it correctly.
Understanding the `out` Keyword in Kotlin Generics
Learn what the `out` keyword means in Kotlin generics, how covariance works, and when to use `out T` with simple examples.
Updating MutableLiveData from Coroutines in Kotlin: setValue vs postValue
Learn why MutableLiveData.setValue fails on background threads in Kotlin coroutines and how to update LiveData safely in Android.
Use @Parcelize Without kotlin-android-extensions in Kotlin
Learn how to migrate from deprecated kotlin-android-extensions Parcelize support to the kotlin-parcelize Gradle plugin and kotlinx.parcelize.Parcelize import.
Use Gson TypeToken with Generic Lists in Kotlin
Learn how to deserialize generic lists with Gson TypeToken in Kotlin, fix constructor access errors, and build reusable JSON helpers.
What `suspend` Means in Kotlin Coroutines
Learn what `suspend` means in Kotlin coroutines, which coroutine is suspended, and how suspension differs from blocking threads.
What the Elvis Operator Does in Kotlin
Learn how Kotlin's Elvis operator (?:) works, how it handles null values, and how it compares to an if expression.
What the `by` Keyword Does in Kotlin: Delegated Properties Explained
Learn what the `by` keyword means in Kotlin, especially for delegated properties in Android and Kotlin apps, with examples and common mistakes.
What to Use Instead of Deprecated Handler() in Android Kotlin
Learn why Handler() is deprecated in Android Kotlin and how to replace it with Handler(Looper), coroutines, or view.postDelayed().
When to Use Inline Functions in Kotlin
Learn when to use inline functions in Kotlin, how lambdas are compiled, and why inline can improve higher-order function performance.
When to Use run, let, apply, also, and with in Kotlin
Learn when to use Kotlin scope functions run, let, apply, also, and with with clear examples, comparisons, mistakes, and a mini project.
Why Kotlin Smart Cast Fails on Mutable Properties: var, Null Safety, and Elegant Fixes
Learn why Kotlin smart cast fails on mutable properties and how to fix it safely using local vals, safe calls, and null handling.
fold() vs reduce() in Kotlin: Difference, Examples, and When to Use Each
Learn the difference between fold() and reduce() in Kotlin with simple examples, execution steps, common mistakes, and when to use each.
launch/join vs async/await in Kotlin Coroutines
Learn the difference between launch/join and async/await in Kotlin coroutines, when to use each, and common mistakes beginners make.