Questions
Kotlin questions
Choose a question page, learn the concept, then test your understanding with a quiz.
How to Fix Incompatible Kotlin Metadata Version in Android When Updating Stripe
Learn why Kotlin metadata version errors happen in Android, how to fix them after updating Stripe, and how to collect email and cardholder name.
How to Fix IntelliJ Kotlin JVM Target Mismatch: 1.8 vs 1.6
Learn why IntelliJ shows a Kotlin JVM target mismatch error and how to align bytecode targets like 1.8 and 1.6 correctly.
How to Fix Jackson "No Creators, like default construct, exist" Error in Java Retrofit Deserialization
Learn why Jackson throws the "No Creators" deserialization error in Java Retrofit apps and how to fix it with constructors and annotations.
How to Fix KAPT "unrecognized Attribute name MODULE" in Android/Kotlin Builds
Learn what causes the KAPT "unrecognized Attribute name MODULE" build error in Android/Kotlin and how to debug version mismatches safely.
How to Fix Kotlin Runtime JAR Version Mismatch Warnings
Learn why Kotlin runtime JAR files must match versions, how classpath mismatches happen, and how to fix them in Gradle projects.
How to Fix android:exported Errors in Android 12 Manifest Files
Learn why Android 12 requires android:exported in manifest components and how to fix merge errors in activities, services, and receivers.
How to Fix minCompileSdk AAR Metadata Errors in Android Java or Kotlin
Learn why Android shows minCompileSdk AAR metadata errors and how to fix them by updating compileSdkVersion and dependencies.
How to Generate a Random Number in Kotlin
Learn how to generate random numbers in Kotlin, including integers in a range, syntax, examples, common mistakes, and practical use cases.
How to Get Context in Jetpack Compose for Toast Messages in Kotlin
Learn how to access Context in Jetpack Compose and show a Toast correctly using LocalContext.current with clear Kotlin examples.
How to Get the Current Index in a for-each Loop in Kotlin
Learn how to get the current index in a Kotlin for-each loop using withIndex(), forEachIndexed(), and simple examples.
How to Get the Current Unix Timestamp in Android Java
Learn how to get the current Unix timestamp in Android Java, including seconds vs milliseconds, examples, pitfalls, and real use cases.
How to Handle Try-with-Resources in Kotlin
Learn the Kotlin equivalent of Java try-with-resources using use(), AutoCloseable, and practical resource-handling examples.
How to Initialize Arrays in Kotlin with Values
Learn how array initialization works in Kotlin, including arrayOf, primitive arrays, syntax examples, and common mistakes for beginners.
How to Initialize an Empty MutableList in Kotlin
Learn how to create an empty MutableList in Kotlin, when to use mutableListOf(), and common mistakes with List vs MutableList.
How to Iterate Over a HashMap in Kotlin
Learn how to iterate over a HashMap in Kotlin with for loops, destructuring, keys, values, and practical examples for beginners.
How to Launch an Activity from Another App in Android Using Intents
Learn how to open an installed app or specific Activity from another Android app using Intents, PackageManager, and safe checks.
How to Null Check in Kotlin: == vs === Explained
Learn the correct way to check for null in Kotlin. Understand == vs ===, != vs !==, and when structural or referential equality matters.
How to Parse JSON in Kotlin: Strings, Objects, and Mapping to Classes
Learn how to parse JSON in Kotlin and map JSON strings to classes using practical examples with Kotlin-friendly JSON libraries.
How to Place the Cursor at the End of an EditText in Android Java
Learn how to keep the cursor at the end of an EditText in Android Java after changing text programmatically.
How to Read Files from src/test/resources in Kotlin
Learn how to read text and HTML files from src/test/resources in Kotlin tests using class loaders and resource streams.