Welcome to the forum.
To give you a quick introduction: Multi-OS Engine allows you to create the iOS version of your app in Java. MOE integrates into Android Studio, IntelliJ or Eclipse, so you can just continue using the tools that you already know.
You can start with the https://multi-os-engine.org/start/ and check out the sample projects in https://github.com/multi-os-engine/moe-samples-java
Sadly, the current docs are a bit outdated, we are working hard on changing that. In the meantime if you have any questions, just ask here on the forum and we will try to help.
You will need a Mac to build the iOS version of your app. We have remote build support integrated into our Gradle plugin that can be used on Windows to build the iOS app on a Mac.
You can launch and debug the java code from your local Java IDE, even when you are on Windows and use Remote build.
MOE is very flexible, and you can do lots of advanced things, like develop a part of your iOS app in Swift or ObjC and integrate them with Java. Or you can automatically generate Java bindings for existing ObjC and Swift libraries that you want to use in your app.
MOE is completely open-source, there are no license fees.