How do I keep third part from seeing my GWT core Java source code

I have the following class in my GWT core library:
@JsExport("MSEP")
@JsType(prototype= "Object" )
public abstract class MyStartEntryPoint implements EntryPoint {
    public void onModuleLoad() {

    }

    public abstract JsData getJsData(final String identifier);
}.

I want to compile my GWT core library into javascript such as gwt.nocache.js so I can use JSNI to wrap the above class and third part can use my JSNI wrapper. The reason why I do this way is to keep third part from seeing my GWT core source code. Is it possible? 
Once I checked the compiled gwt.nocache.js, I could not find any token like 'MSEP'. Thank you very much in advance.

David.

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