jni trouble

[stef]

Hi guys,
Could U tell me where is my error with my little JNI calling :

with VC 6 and JAVA 1.5.2
(i omitted the package/import declaration to gain time)

//--------------------------------------- C method : (generating a test.dll)

JNIEXPORT void JNICALL Java_com_pack_JTest_Connect(JNIEnv *env, jobject
this, jstring Str)
{
jfieldID fid;
jclass cls;
jlong val;

cls = (*env)->GetObjectClass(env, this);
fid = (*env)->GetFieldID(env, cls, "m_hdl", "J");

val = (*env)->GetLongField(env, this, fid);
(*env)->SetLongField(env, this, fid, 666);
}


//--------------------------------------- Java
public class JTest
{
private long m_hdl;

static
{
try
{
System.loadLibrary("test");
}
catch (java.lang.UnsatisfiedLinkError e)
{
System.out.println("error : " + e);
}
}


public static native void Connect( String xmlConnect );


/*
*
*/
public JTest()
{
Connect("");
System.out.println("Test : "+m_hdl);
}
}


Simple no ?
and with a little test like


class main
{
public static void main(String[] args)
{
JTest p;
int i=0;

p = new JTest();
p.Connect("");
}
}


I get :
Exception in thread "main" java.lang.NoSuchFieldError: m_hdl
at com.pack.JTest.Connect(Native Method)
at com.pack.JTest.<init>(JTest.java:35)
at main.main(main.java:18)

As I can see in debug mode, method GetFieldID() doesn't "see" m_hdl !!!!
why ???



thanx for your help

 

[Gordon Beaton]

JNIEXPORT void JNICALL Java_com_pack_JTest_Connect(JNIEnv *env, jobject
this, jstring Str)
{
jfieldID fid;
jclass cls;
jlong val;

cls = (*env)->GetObjectClass(env, this);
fid = (*env)->GetFieldID(env, cls, "m_hdl", "J");

val = (*env)->GetLongField(env, this, fid);
(*env)->SetLongField(env, this, fid, 666);
}

public static native void Connect( String xmlConnect );

I get :
Exception in thread "main" java.lang.NoSuchFieldError: m_hdl
at com.pack.JTest.Connect(Native Method)
at com.pack.JTest.<init>(JTest.java:35)
at main.main(main.java:18)

As I can see in debug mode, method GetFieldID() doesn't "see" m_hdl !!!!
why ???

You have declared the native method using "static", so the second
argument to the native method isn't "this" as you seem to expect, it's
an object representing the JTest *class*.

You then do GetObjectClass() which returns an object representing
java.lang.Class. It doesn't contain the field you're looking for.

The solution is to remove the static declaration from the native
method.

/gordon