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Flutter vs. Kotlin: Which Is Best for Cross-Platform App Development?

Serhii Osadchuk, CTO @ DOIT Software
Serhii Osadchuk, CTO @ DOIT Software

Once upon a time, Flutter and React Native were the go-to programming solutions for building cross-platform apps. Over the last decade, however, Kotlin has emerged as a new Java-based programming language, and mobile app developers around the world are taking notice.

Flutter and Kotlin offer developers different tools and features, so which should you learn and use? Since Flutter is an open-source UI software development kit and Kotlin is a general-purpose programming language, it's hard to contrast the two—it's like comparing apples to oranges. To help you better understand which tool is best for your use case, let's take a look at the pros, cons, and nuances of both.

Flutter App Development Analysis

Flutter is a Google-built UI toolkit that allows you to build a native mobile app with a single codebase. It enables app developers to build two different apps for IOS and Android using one programming language. Also, Flutter can be used to build macOS and is currently being beta tested for web apps. To build with Flutter, you'll use Google's programming language, Dart.

Pros of Using Flutter

1. Easy to Use
The Flutter-Dart coding combo is easy to use and quick to learn. If you've ever coded with Swift, React Native, or Java, you'll feel the difference with Flutter's modern framework. You can create fully functional apps with significantly less code.

2. Open-Source and Free
Because Flutter and Dart are both open-source, you'll get free access to the original code and all the documentation you need. Flutter's documentation is user-friendly and easy to navigate, making it quick and simple to find answers to all your questions.

3. See Output in Real-Time
Flutter empowers you to edit your code and watch the changes in real-time through functionality called Hot Reload. Hot Reload allows you to make changes to the back-end and observe the front-end changes instantly, decreasing the need to frequently reload the entire app. This functionality saves teams valuable development and compilation time.

4. Growing in Popularity
Flutter isn’t as widely adopted yet, but it’s quickly growing in popularity. Dart is swiftly becoming one of the most popular programming languages, and Flutter received first place by GitHub issues among other cross-platform development technologies. While Flutter isn’t as popular in the United States as it is in other countries, it’s on a fast track to becoming a go-to option for programmers in many fields of development.

5. Great Native Support
While Flutter’s Native support isn’t perfect, developers are in love with the technology. One states, “Flutter takes care of things like scrolling speed, so it feels as close to native Android/iOS app as possible.”

Cons of Using Flutter

1. Not as Widely Adopted
While developers enjoy Flutter's modern framework, there aren't as many educational resources and classes for up-and-coming coders because Dart is less popular than Kotlin, Java, JavaScript, C#, and C. As of now, there are only 15 courses on Udemy that teach Flutter, while there are at least 40 that teach Kotlin. This can cause hiring and training slowdowns. However, Flutter’s fast-growing popularity could negate this con in no time.

2. Large App Sizes
Flutter-built apps are relatively big, and this is a problem for developers who are trying hard to build apps that won't take up too much space on limited IOS and Android devices.


Kotlin App Development Analysis

Kotlin is an open-source, statically typed programming language designed to interoperate with Java. As a standalone language, it provides excellent features over Java, but it also works well in conjunction with the older language. Kotlin's multiplatform capabilities allow developers to share code, logic, and data across several platforms: IOS, Android, Web, and more.

Pros of Using Kotlin

1. Works Well with Java
Since Kotlin preserves a good portion of Java's object-oriented nature, it's straightforward to convert any pre-existing Java code.

2. Clear and Concise Code
Kotlin's straightforward syntax makes your code more clear and compact. Less time writing fewer lines of code makes your development team more efficient, saving you valuable time and money.

3. Safe and Consistent
Because your codebase is shorter and easy-to-read, bugs are compiled in the development process, so errors are spotted and fixed early on.

Cons of Using Kotlin

1. Relatively New Language
While Kotlin and Java share several similarities, hiring a Java developer is not the same as recruiting a Kotlin-savvy coder. Because the programming language is relatively new, the current hiring demand greatly exceeds the number of available Kotlin developers. On LinkedIn, for example, there are over 3,000 job openings looking for developers with Kotlin experience, while there are less than 500 job openings looking for Flutter experience.

2. More Expensive
Because the Kotlin SDK offers semi-native functionalities, the cost of building a mobile app skyrockets. Kotlin's price consequences make it an expensive programming language, especially when building prototypes and MVPs.

3. Slower Compilation Speed
In rare cases, Kotlin beats Java in compilation speeds, but it's frequently much slower. When compiling incremental changes, Kotlin does a decent job, but it's still not as quick as some of the other modern options, like Flutter.

4. Weak Support of Native
Currently, Kotlin isn’t very supportive of Native. While the Kotlin/Native product is expanding, it’s still lacking features developers need, like a Kotlin-based, platform-independent GUI.

Flutter vs. Kotlin: The Final Verdict
There's no best choice when it comes to Flutter or Kotlin — you'll need to decide based on your unique case, team, and potentially existing codebase. Both Kotlin and Flutter are supported by Google, so you can't go wrong.

If you’re a startup with a smaller team, Flutter is a great low-cost choice because it allows you to create multiple apps with one codebase—requiring less time and fewer developers. Kotlin, however, is a great choice if you’re working with any pre-existing Java code, but keep in mind it’ll be harder to find experienced developers.

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