Open Source Java Runtimes for Apple iPhone

Capacitor is an open source native runtime for building Web Native apps. Create cross-platform iOS, Android, and Progressive Web Apps with JavaScript, HTML, and CSS. Capacitor’s native plugin APIs make it extremely easy to access and invoke common device functionality across multiple platforms. Build web-based applications that run equally well across iOS, Android, and as Progressive Web Apps. Access the full Native SDKs on each platform, and easily deploy to the App Stores (and the web). Add custom native functionality with a simple Plugin API, or use existing Cordova plugins with our compatibility layer. Capture images, save photos, and configure hardware parameters like saturation and color balance. Save and read documents, assets, and other content your users need to access via native file systems. Gather critical information about a user’s device location, such as latitude and longitude.

J2ObjC is an open-source command-line tool from Google that translates Java source code to Objective-C for the iOS (iPhone/iPad) platform. This tool enables Java source to be part of an iOS application's build, as no editing of the generated files is necessary. The goal is to write an app's non-UI code (such as application logic and data models) in Java, which is then shared by web apps (using GWT), Android apps, and iOS apps. J2ObjC supports most Java language and runtime features required by client-side application developers, including exceptions, inner and anonymous classes, generic types, threads and reflection. JUnit test translation and execution is also supported. J2ObjC cannot convert Android binary applications. Developers must have source code for their Android app, which they either own or are licensed to use.