What is mobile?

OpenJDK Mobile is a project that brings Java to iPhones and iPads. It lets developers take Java applications and run them on iOS, a platform that has historically not had native support for Java. This opens the door for existing Java codebases to reach Apple mobile users without requiring a complete rewrite in a different programming language. At a technical level, the project adapts the standard Java Development Kit (the engine that runs Java programs) to work within Apple's strict rules for mobile apps. Because iOS prevents apps from using certain memory features that Java traditionally relies on, the project uses a specific configuration called "Zero" to get around this limitation. Developers configure and compile the toolkit on a Mac, using Apple's standard Xcode software, which produces a package containing the core Java engine ready to be embedded inside an iOS app. The primary audience for this tool consists of Java developers and software companies who already have Java applications or backend systems and want to bring them to iOS devices. For example, a company with an enterprise application written in Java could use this to ship a version that runs directly on an employee's iPad, rather than requiring a constant internet connection to a remote server. It is also useful for teams who want to test their Java software on the iOS simulator before deploying to actual hardware. One notable tradeoff the project makes is in performance. Because it must use the "Zero" JVM variant to comply with iOS security restrictions, it sacrifices the speed optimizations found in the standard desktop or server versions of Java. However, for testing purposes on the iOS simulator, developers can switch to faster variants that take advantage of the more permissive environment of a developer machine.