Return object from java native method

Question

I would like to call a method through a native java interface, which returns an object.

This is my native method

public native Node getProjectionPoint(double lat, double lon);

Node class

 public class Node {        
    private String id;
    private double latitude;
    private double longitude;
}

C header file

JNIEXPORT jobject JNICALL Java_org_smartcar_serverdatainterface_shared_services_CppConnector_getProjectionPoint (JNIEnv *env, jobject obj, jdouble lat, jdouble lon);

How could I create an object and return it to java?

Take a look to : stackoverflow.com/a/4325678/3315914

rpax
– rpax

2014-03-10 13:04:11 +00:00
Commented Mar 10, 2014 at 13:04 — rpax
– rpax, Commented Mar 10, 2014 at 13:04

JanithOCoder · Accepted Answer · 2014-03-10 18:22:50Z

7

I sort out the problem

JNIEXPORT jobject JNICALL Java_org_smartcar_serverdatainterface_shared_services_CppConnector_getProjectionPoint
  (JNIEnv *env, jobject obj, jdouble lat, jdouble lon)
{
    jclass class = (*env)->FindClass(env,"org/smartcar/serverdatainterface/shared/businessentities/Node");

    if (NULL == class)
        PrintError ("class");

    jmethodID cid = (*env)->GetMethodID(env,class, "<init>", "(DD)V");

   if (NULL == cid)
       PrintError ("method");

   return (*env)->NewObject(env, class, cid, lat, lon);
}

this works perfectly

answered Mar 10, 2014 at 18:22

JanithOCoder

3013 gold badges5 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

ebasconp · Accepted Answer · 2014-03-10 13:22:14Z

3

In JNI you have a method

JNIEnv->NewObject() that invokes the actual constructor of a given Java class.

Maybe something like:

JNIEXPORT jobject JNICALL Java_org_smartcar_serverdatainterface_shared_services_CppConnector_getProjectionPoint (JNIEnv *env, jobject obj, jdouble lat, jdouble lon)
{
  jclass cls = env->GetObjectClass(obj);
  jmethodID constructor = env->GetMethodID(cls, "<init>", "(DD)V");
  return env->NewObject(cls, constructor, lat, lon);
}

You should modify your class constructor to receive two parameters. You can also initialize field by field, but it requires to invoke GetFieldID two times in C++.

edited Mar 10, 2014 at 13:22

answered Mar 10, 2014 at 13:13

ebasconp

1,6682 gold badges17 silver badges27 bronze badges

7 Comments

rpax Over a year ago

Buff... Maybe it's better to copy it, don't you think?

ebasconp Over a year ago

Sorry, I misunderstood your question; I edited my answer accordingly.

JanithOCoder Over a year ago

I'm getting this error "error: request for member 'GetObjectClass' in something not a structure or union"

ebasconp Over a year ago

Are you including jni.h ?

Tom Blodget Over a year ago

GetObjectClass would work in this case because the method is an instance method in the same class as the object to be created. I would find it confusing. FindClass is clearer.

|

Collectives™ on Stack Overflow

Return object from java native method

2 Answers 2

Comments

7 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

7 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related