Questions
Kotlin questions
Choose a question page, learn the concept, then test your understanding with a quiz.
How to Debug “Unfortunately, MyApp Has Stopped” in Android
Learn how to diagnose and fix the Android “Unfortunately, app has stopped” crash using Logcat, stack traces, and debugging steps.
How to Diagnose ':app:compileDebugKotlin' Compilation Errors in Android Gradle Builds
Learn how to troubleshoot Android ':app:compileDebugKotlin' errors by reading the real compiler output and checking Gradle and Kotlin setup.
How to Fix Deprecated Gradle Features Used in This Build for JUnit 5 and Android Gradle
Learn why deprecated Gradle features appear with JUnit 5 and Android builds, and how to diagnose and fix them safely.
How to Fix Duplicate Kotlin Stdlib Class Errors in Android Gradle
Learn why duplicate Kotlin stdlib class errors happen in Android and how to fix version conflicts in Gradle dependencies safely.
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 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 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 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 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 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 Set Text in an EditText in Kotlin
Learn why EditText.text expects Editable in Kotlin and how to correctly set and read text using setText(), text, and toString().
How to Use break and continue with forEach in Kotlin
Learn why break and continue do not work directly in Kotlin forEach, and how to use labels, returns, and regular loops instead.
How to Vibrate an Android Device in Java: Vibrator and VibrationEffect
Learn how to make an Android device vibrate in Java using Vibrator and VibrationEffect, including patterns, permissions, and common pitfalls.
Java Static Methods in Kotlin: Equivalents and Best Practices
Learn how Kotlin replaces Java static methods using top-level functions, companion objects, and objects with clear examples.