JNI 的GetMethodID

[lvxn_sina]

jobject _java_integer(JNIEnv* jenv, jint val)
{
jclass jcls;
jmethodID jmid;
jobject jobj;

jobj = ((jcls=(*jenv)->FindClass(jenv, "java/lang/Integer")) != NULL
&& (jmid=(*jenv)->GetMethodID(jenv, jcls, "", "(I)V")) != 0) ?
(*jenv)->NewObject(jenv, jcls, jmid, val) : NULL;
(*jenv)->ExceptionClear(jenv); /* not raise exception */
return jobj;
}

为什么GetMethodID就是得不到id呢？
GetMethodID(jenv, jcls, "Integer", "(I)V")
GetMethodID(jenv, jcls, "", "(I)V ")
GetMethodID(jenv, jcls, "Integer", "(I)V ")
都不可以！