When comparing Kotlin vs B4X, the Slant community recommends B4X for most people. In the question“What are the best ways to make a cross-platform application?” B4X is ranked 2nd while Kotlin is ranked 13th.
Ranked in these QuestionsQuestion Ranking
Pro Great tooling support
Since Kotlin is made by Jetbrains (the developers of IntelliJ IDEA) so it stands to reason that the IntelliJ support for Kotlin is also great. Besides that, Kotlin also works well with existing Java tools such as Eclipse, Maven, Gradle, Android Studio, etc...
Pro Easy adoption for existing Java programmers
Kotlin runs on the JVM and Java interoperability has been one of the main objectives since the language was born. It runs everywhere Java does; web servers, mobile devices (Android), and desktop applications. It also works with all the major tools in the Java ecosystem like Eclipse, IntelliJ, Maven, Ant, Gradle, Spring Boot, etc.
All of this makes adoption extremely easy even for existing Java projects. On top of this there's also ensured Type safety and less boilerplate code needed.
Pro Easy to learn if you have prior programming experience
Kotlin's syntax is extremely easy to understand. The language can be picked up in a few hours just by reading the language reference.
Pro No runtime overhead
The standard library is relatively small and tight. It mostly consists of focused extensions of the Java standard library and as such adds no additional runtime overhead to existing Java projects.
Pro Officially supported for Android development
Starting with version 3.0 of Android Studio, Kotlin support will be built-in. This means that it's now easier than ever to use Kotlin for existing Android projects or even start writing Android apps only with Kotlin from scratch.
This also means that Kotlin and Kotlin plugins for Android Studio will be fully supported in the future and their likelihood of being abandoned is quite small since Google is fully embracing the language for their Android ecosystem (alongside Java and C++).
Pro Low-risk adoption for existing Java codebases
Since it has such a good interoperability with Java, Java libraries, and Java tools. It can be adopted for an existing Java codebase at little to no cost. The codebase can be converted from Java to Kotlin little by little without ever disrupting the functionality of the application itself.
Pro Does not impose a particular philosophy of programming
It's not overly OOP like Java and it does not enforce strict functional paradigms either.
Pro Is built to solve industrial problems
Kotlin has been designed and built by developers who have an industrial background and not an academic one. As such, it tries to solve issues mostly found in industrial settings. For example, the Kotlin type system helps developers avoid null pointer exceptions. Reasearch languages usually do not have
null at all, but APIs and large codebases usually need
Pro A very active forum where you can find any issue you have, and quick answers to new ones
Pro Live code swapping
A huge productivity boost when you can run your apps on the devices and make code changes real time without needing to recompile.
Pro A highly motivated program author who is very active in the forums
Erel Uziel is simply the most pro-active Soft-Creator/Forum Manager you will ever come across. If it has not yet been asked & answered, just ask and you will be answered withing minutes, and thanks to it being a trully international forum, this is achieved 24h/7d.
Pro Create easy, fast and with less code cross-platform views
B4XUI custom views are designed, by Erel and other forum members, exactly with this in mind; custom views that act and feel exactly the same no matter what platform you target.
Pro Very easy to use and powerful for IoT
Support for Bluetooth/BLE, MQTT, TCP/UDP, Serial, NFC, Websockets, HTTP/2 across platforms makes it the ideal tool for IoT projects.
Pro Powerful general purpose programming tool
As mentioned in its website, "With B4X, anyone who wants to, can develop real-world solutions."
Pro No complexities compared with other tools
No need to learn JAVA, C+, PHP, or any other complementary languages in order to achieve exactly what you need.
Pro Many informative video tutorials
The tutorials help beginners as well as more experienced programmers grasping important concepts.
Pro The best tool with the best service by Erel
Con May be hard for programmers already used to imperative style to learn functional programming from Kotlin
Since Kotlin does not enforce any particular paradigms and is not purely functional, it can be pretty easy to fall back to imperative programming habits if a programmer comes from an imperative background.
Con The need for Java interoperability has forced some limitations
The need to make Kotlin interoperable with Java has caused some unintuitive limitations to the language design.