Need some clarification in using JNI

I want to pass string to function(in C) which returns jobject.
public static native HashMap<string, string> displayString(java.lang.String value);
public static native HashMap<string, string> displayString();

I declared the native methods in java as above. The problem is C is not accepting the string and pass the hashmap at the same time.

My c function is like this:
JNIEXPORT jobject JNICALL Java_JavaNative_displayString(JNIEnv* env, jclass obj, jstring str) {
return jobject;
}

jobject is a hashmap. It works fine, that is why I didn't add the code. My c code reads the file,add it to hashmap and then returns it.