What Is Kotlin, and Why Do Android Apps Use It?
Kotlin is to Android what a well-made power drill is to a carpenter. The old hand drill (Java) still works, but the new one does the same job with less effort and fewer slips.
Kotlin, explained simply
A programming language is how developers write instructions for a computer. Kotlin was created by JetBrains, a company known for developer tools. It is free and open source.
In 2019, Google announced that Android development would be "Kotlin-first". That means Google's new Android tools, guides and code samples are written with Kotlin in mind. Before Kotlin, most Android apps were written in Java, and Java is still supported.
How Kotlin works
Kotlin code is turned into the same kind of instructions that Java produces. That has a big practical benefit: Kotlin and Java can live side by side in one app. A team with an old Java app can write new features in Kotlin without rewriting everything.
Kotlin was built to avoid common mistakes. The best-known example is the "null" error, where code tries to use something that is empty. In Java this is a frequent crash. Kotlin forces developers to handle empty values on purpose, so many of these crashes never happen.
Kotlin also has coroutines, a simple way to do slow jobs, like loading data from the internet, without freezing the screen. Users feel this as an app that stays smooth while it works.
What Kotlin is good for
- Native Android apps, which is its main job.
- Apps that use Android-only features, like home screen widgets, background services, wearables and car apps.
- Android-first markets, where most of your users carry Android phones.
- Server code: Kotlin can also power backends, though this is less common than mobile.
- Sharing logic with iOS through Kotlin Multiplatform, where the business rules are shared but each app keeps its own screens.
When Kotlin is not the best fit
- You need Android and iOS at launch on a small budget. Native Kotlin covers Android only, so iOS becomes a second project, usually in Swift.
- Your app is mainly simple screens and forms, which a cross-platform tool like Flutter handles well with one team.
- You plan to have one small team maintain everything for years. Two native apps need two sets of skills.
Kotlin vs Java vs Flutter for Android
| Kotlin | Java | Flutter (Dart) | |
|---|---|---|---|
| Google's current stance | Recommended first | Still supported | Google's cross-platform toolkit |
| Code length | Short | Longer | Short |
| Built-in crash protection for empty values | Yes | No | Yes |
| Covers iOS too? | Only shared logic, via Multiplatform | No | Yes, full app |
| Best for | Polished native Android | Maintaining older apps | One app for both stores |
What Kotlin means for cost and timeline
For an Android-only app, Kotlin is the most direct route, and Google's newest tools assume you use it. Developers are easy to find, especially in India, where Android work is very common.
The cost question is really native vs cross-platform. Native Kotlin plus native Swift gives you the best fit on each platform but roughly two builds to pay for and maintain. A cross-platform app costs less to run long-term but may need small native add-ons for special features.
Kotlin also makes code reviews quicker. Shorter code is easier for a second developer to read and check, which helps catch problems before they reach your users.
If you have an older Java app, you do not need a full rewrite. Moving to Kotlin step by step, screen by screen, is normal and keeps costs spread out.
How Appryze uses Kotlin
We build Android apps and use Kotlin when a project needs native Android features, and for the native pieces inside Flutter apps. Each build comes with free Google Play submission and a month of launch marketing. Read more on our app development page, or visit the official Kotlin site. Kotlin pairs naturally with Jetpack Compose for screens.
Common questions
Is Kotlin better than Java for Android?
For new Android apps, most teams choose Kotlin. It needs less code, protects against common crashes and is Google's recommended language. Java still works and still gets support, so older Java apps are fine; they can add Kotlin gradually instead of being rewritten.
Can Kotlin build iPhone apps?
Partly. With Kotlin Multiplatform, a team can share business logic, like data handling and rules, between Android and iOS. The iPhone screens can stay native in SwiftUI or be shared with JetBrains' Compose Multiplatform. It is a growing option, but less common than Flutter or React Native.
Who owns Kotlin?
Kotlin was created by JetBrains and is open source. JetBrains and Google co-founded the Kotlin Foundation to look after the language's future. You can use Kotlin for free in commercial apps.
Do I need Kotlin if I build with Flutter?
Usually only a little. A Flutter app is written in Dart, but when it needs a special Android feature with no ready-made plugin, developers write a small native piece in Kotlin and connect it to the Flutter app.
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