You already have an Android app. It owns the data — vehicle telemetry, sensor state, transactional records — and exposes it through a Java or Kotlin service layer. Now product wants a richer surface on top: a 3D instrument cluster, an operator dashboard, a kiosk experience that needs more than the standard Android UI toolkit gives you. The natural answer is to add an Unreal Engine app as a rendering tier — a second process that draws the HMI and reaches back into your existing Java service for the data it visualizes.

That's a cross-process Android problem with a Java service host on one end and a C++ engine consumer on the other. Bind a Service, write a Messenger handler, define a Parcelable for every payload, hand-roll a JNI surface so the engine's C++ can call into the Java client, then keep the method signatures in sync forever. ApiGear's new Java template ships the Android counterpart to the Unreal Engine template's new JNI feature, which generates both a JNI client (for consuming an Android service) and a JNI adapter (for exposing one). Define your interface once, generate both sides, and the Messenger plumbing, parcels, and JNI bindings appear together. This post walks through the realistic case — Android app hosts the service, UE app consumes it — and shows what comes out of the generator.

What if you could describe an API in plain English and your AI assistant would design the interface, validate it, and generate a production-ready SDK — all without leaving your editor?

That's exactly what happens when you connect ApiGear to your AI coding assistant via MCP. No spec syntax to learn, no CLI commands to memorize. You describe what you need, and your assistant handles the rest — from API design to generated code.

An API surface is the public interface of an object which is exposed to users of the object. The API surface is defined by an IDL and defines the contract between the user and the implementer of an object.