New primitive JNI types

Question

How can we use the new primitive types in JNI. I have a function that returns a jobject . You can return jint , jchar , etc.

There is a NewString , why not NewInteger , NewCharacter , NewDouble , etc. At the moment, there is no autoboxing at the JNI level.

I can go with a call to NewObject , but for creating primitive types this would be too much overhead.

 jobject NewInteger(JNIEnv* env, jint value) { jclass cls = FindClass(env, "java/lang/Integer"); jmethodID methodID = GetMethodID(env, cls, "<init>", "(I)V", false); return env->NewObject(cls, methodID, value); } 

I have wrapper functions to get Class and MethodID.

Answer 1

jint , jdouble , etc. not jobjects . As you say, these are primitive variables. Just fill them out!

 jint someInt = 1; jdouble someDouble = 3.14159; 

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Re edit: I see you want to return types in a box, such as Integer , Double , etc. Yes, you are probably the posting method you posted is the way to go.

Answer 2

Why do you feel that this approach is “too much overhead”? If you want to return a value in a box (which is an object containing a primitive, not a "primitive type"), you need to create this object.

One option is to call the valueOf() method on a shell type.

However, I think that you'd better return the actual primitive value and let it get the box (if you need it) after it is on the Java side.

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If you are worried about the overhead of finding a function / constructor, you should cache the method identifiers. Unlike object pointers, they won't change (with some caveats that unload classes that don't apply to primitive wrappers). See Clause 10.7 here: http://java.sun.com/docs/books/jni/html/pitfalls.html