Jvalue

jvalue is a union type used in the Java Native Interface (JNI) to pass arguments from native code to Java methods. Defined in the JNI header jni.h, it can hold every Java value that can be passed as a parameter, including all primitive types and object references. The fields typically named z, b, c, s, i, j, f, d, and l correspond to boolean, byte, char, short, int, long, float, double, and a Java object reference (jobject), respectively. Only one field in each jvalue element is valid at a time.

In practice, jvalue is used with the A-variant JNI calls, such as Call<Type>MethodA, CallStatic<Type>MethodA, and NewObjectA. Arguments are supplied as an array of jvalue, with one element per parameter. Before calling, each element is filled with the appropriate value using the corresponding field. The return value of the Java method is obtained through the specific Call<Type> method; the jvalue array is used solely for input parameters.

Example:

jvalue args[2];

args[0].i = 42;

args[1].l = someObjectRef;

(*env)->CallVoidMethodA(env, obj, methodID, args);

Notes: Use the correct field for each parameter type and ensure the array remains valid for the duration of the call. The jvalue union provides a convenient way to represent heterogeneous argument lists when interfacing native code with the Java VM.