Using JNI can we pass custom data types from Java to C (or vice versa)? I see a mapping of primitive datatypes to types in C however not too sure if we can send across our own data types (e.g. Send across or return an Employee object or something!).
+1
A:
You can. If you want to make Java/C translation easier, check out Swig, which allows you to translate between Java and C/C++ structures in a straightforward fashion..
Brian Agnew
2010-03-23 23:26:57
A:
You can use JNA to easily pass structures around. JNA allows you to write your binding completely in Java code. :-)
Chris Jester-Young
2010-03-23 23:52:36
+2
A:
If you're going to be doing this with a lot of objects, something like Swig would be best. You could use jobject type to pass around custom objects. The syntax isn't nice, perhaps there is a better way to write this.
Example Employee object:
public class Employee {
private int age;
public Employee(int age) {
this.age = age;
}
public int getAge() {
return age;
}
}
Call this code from some client:
public class Client {
public Client() {
Employee emp = new Employee(32);
System.out.println("Pass employee to C and get age back: "+getAgeC(emp));
Employee emp2 = createWithAge(23);
System.out.println("Get employee object from C: "+emp2.getAge());
}
public native int getAgeC(Employee emp);
public native Employee createWithAge(int age);
}
You could have JNI functions like this for passing an employee object from Java to C, as a jobject method argument:
JNIEXPORT jint JNICALL Java_Client_getAgeC(JNIEnv *env, jobject callingObject, jobject employeeObject) {
jclass employeeClass = (*env)->GetObjectClass(env, employeeObject);
jmethodID midGetName = (*env)->GetMethodID(env, employeeClass, "getAge", "()I");
int age = (*env)->CallIntMethod(env, employeeObject, midGetName);
return age;
}
Passing an employee object back from C to Java as a jobject, you could use:
JNIEXPORT jobject JNICALL Java_Client_createWithAge(JNIEnv *env, jobject callingObject, jint age) {
jclass employeeClass = (*env)->FindClass(env,"LEmployee;");
jmethodID midConstructor = (*env)->GetMethodID(env, employeeClass, "<init>", "(I)V");
jobject employeeObject = (*env)->NewObject(env, employeeClass, midConstructor, age);
return employeeObject;
}
Stew
2010-03-24 02:15:34