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# jni

Java Native Interface bindings. The package provides `#[repr(C)]` mirrors of the JVM's `jni.h` dispatch tables — `JNINativeInterface` (the `JNIEnv` function table) and `JNIInvokeInterface` (the `JavaVM` table) — plus the `jint` / `jlong` / `jobject` type aliases.

The JVM hands you a pointer to one of these tables; you read a function pointer out of it and call it through `env`, exactly as C's `(*env)->FindClass(env, ...)` does:

```cplus
import "jni/jni" as jni;

fn get_version(env: jni::JNIEnv) -> jni::jint {
    let f: fn(jni::JNIEnv) -> jni::jint = unsafe { (*env).GetVersion };
    return unsafe { f(env) };
}
```

The table is **complete**: all 233 slots of the JNI 1.6 function table, verified field-for-field against the NDK's `jni.h`, so object arrays, `RegisterNatives`, `ExceptionCheck`, `NewDirectByteBuffer`, and the rest are all callable. A layout `#[test]` pins the table sizes so a dropped or mistyped field is caught immediately.

One subtlety the package gets right: `JNIEnv` is modeled as the **double pointer** JNI actually requires (`JNIEnv = *JNINativeInterface`, and native methods receive `*JNIEnv`) — passing the bare table pointer instead trips an ART abort at runtime. This is also the smallest demonstration that `cpc` handles function-pointer struct fields and a self-referential pointer type. It is the foundation [android_view](/docs/packages/android_view) builds on.