GetMethodID of constructor of Java object-CodePudding

I have a short question related to the GetMethodID() function of C . I have been searching for the answer here on StackOverflow, but could not find it. My main code is in Java, but for some parts I would need C . The code below is a simplification of what I intend to implement, to test out how to retrieve and pass objects between Java and C . The final issue is presented at the end of this pos. First, I present the implementation.

public class ExampleJNI {

static {
    System.loadLibrary("nativeObject");
}

public static void main(String[] args){
     ExampleJNI tmp  = new ExampleJNI();
     Order o = tmp.createOrder(1,2,3,4);

     if (o != null){
         System.out.println(o.toString());
     } else {
         System.out.println("Errors present");
     }
}

// Try passing a list
public native Order createOrder(int a, int b, int c, int d);

}

The order class is defined to be:

public class Order {

// Order attributes
public final int a;
public final int b;
public final int c;
public final int d;

private int e;

public Order(int a, int b, int c, int d){
    this.a = a;
    this.b = b;
    this.c = c;
    this.d = d;
}

@Override
public String toString(){
    return a "," b "," c "," d;
}
}

I have the following implementation in C .

#include "ExampleJNI.h"
#include <iostream>
#include <vector>
/*
 * Class:     ExampleJNI
 * Method:    createOrder
 * Signature: (IIII)LOrder;
 */
JNIEXPORT jobject JNICALL Java_ExampleJNI_createOrder(JNIEnv* env, jobject thisObject,     jint a, jint b, jint c, jint d){

// Get a class reference for Order
jclass cls = env->GetObjectClass(thisObject);

if (cls == NULL){
    std::cout << "Class not found" << std::endl;
    return NULL;
}

// Get the method ID of the constructor whick takes four integers as input
jmethodID cid = env->GetMethodID(cls, "<init>", "(IIII)V");

if (cid == NULL){
    std::cout << "Method not found" << std::endl;
    return NULL;
}

return env->NewObject(cls, cid, a, b, c, d);
}

When I run the code, "Method not found" is printed, which indicates that something is going wrong when calling the GetMethodID. I also retrieve the following exception error:

Exception in thread "main" java.lang.NoSuchMethodError: <init>
    at ExampleJNI.createOrder(Native Method)
    at ExampleJNI.main(ExampleJNI.java:11)

Any suggestions on what I should have instead of the <init> are highly appreciated!

CodePudding user response：

thisObject is a ExampleJNI not a Order so GetObjectClass will return ExampleJNI which doesn't have the constructor you are looking for. Change GetObjectClass to env->FindClass("Order").