rosjava services AddTwoInts basic question

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Hello,

I'm looking at the client code (also the server) of AddTwoInts .. and I came across this code:

ServiceClient<rosjava_test_msgs.AddTwoIntsRequest, rosjava_test_msgs.AddTwoIntsResponse> serviceClient;

now my question is, who supplies the implementation of AddTwoIntsRequest and AddTwoIntsResponse ? They are interfaces, with methods such as setA , setSum, etc.. but I can't find an implementation for these methods anywhere..