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  1. #1
    H_P is offline Member
    Join Date
    Jan 2010
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    Default JNI accessing non primitive data type


    I have a JNI method to access java method which returns an Integer object. I do not want to return the primitive int type because this code will be modified to handle Generic objects. The following is what I have. I am not able to get the value of the Integer that I pass. The output at C++ side is something like
    Java Code:
        value = 0x4016f3d0
    How can I get the actual value of Integer object that I pass at C++ end?

    Please help.




    Java Code:
        JNIEXPORT void JNICALL Java_GenericPeer_print (JNIEnv *jenv, jclass jcls, jobject data){
         jclass peerCls = jenv->GetObjectClass(data);
         jmethodID mGetValue = jenv->GetMethodID(peerCls, "getValue","()Ljava/lang/Integer;");
         if(mGetValue == NULL){
           return (-1);
         jobject value = jenv->CallObjectMethod(data, mGetValue);
         cout<<"value = "<<value<<endl;

    Java Code:
    public class GenericPeer {
        	public static native void print(Data d);
        	static {

    Java Code:
    public class Data {
        	private Integer value;
        	pubilc Data(Integer v){ 
        		this.value = v;
        	public Integer getValue() { return value; }
           	public void setValue(Integer value) {
        	this.value = value;
        } (Main class)

    Java Code:
    public class Test {
        	public static void main(String[] args){
               Integer i = new Integer(1);
        		Data d = new Data(i);

  2. #2
    toadaly is offline Senior Member
    Join Date
    Jan 2009
    Rep Power


    The Integer class is not native. It's byte code. There is no acceptable way to access it as a c++ class except to write a c++ wrapper that makes jni calls back to the java world. The only other option is to write a byte code interpreter (or buy one, or partner with someone who has one).

    If you can explain your motivation for wanting the equivalent of *value, we might be able to help you come up with a different way of satisfying that objective.

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