<Request>
    <SpecificRequest>
         <UniqueID></UniqueID>
             or
         <Password></Password>
    </SpecificRequest>
</Request>

<Request>
     <SpecificRequest>
        <mData class="com.example.package.UIDData">
           <UniqueID>6252859A</UniqueID>
        </mData>
     </SpecificRequest >
</Request>

@Root(name = "Request")
public class Request {
    @Element(name = "SpecificRequest")
    private SpecificRequest mSpecificRequest;

    public Request(SpecificRequest specificRequest) {
        mSpecificRequest = specificRequest;
    }
}

public class SpecificRequest {
    private Data mData;

    public SpecificRequest(Data data) {
        mData = data;
    }
}

public abstract class Data {
    private Type mType = Type.None;

    protected Data(Type type) {
        mType = type;
    }

    // other abstract stuff
}

public class UIDData extends Data {
    @Element(name = "UniqueID")
    private String mUID;

    public UIDData(String UID) {
        super(Type.UID);
        mUID = UID;
    }
}

public class TestClass {

    public static void main(String[] args) throws Exception {
        Data data = new UIDData("some UUID value ");
        SpecificRequest specificRequest  =  new SpecificRequest(data);
        Request request = new Request(specificRequest);
        System.out.println(XmlUtils.getXmlBody(request, new RegistryMatcher()));
    }
}
@Root(name = "Request")
class Request {
    @Element(name = "SpecificRequest")
    private SpecificRequest mSpecificRequest;

    public Request(SpecificRequest specificRequest) {
        mSpecificRequest = specificRequest;
    }
}
class SpecificRequest {
 @Element(type = UIDData.class)
    private Data mData;

    public SpecificRequest(Data data) {
        mData = data;
    }
}

abstract class Data {
    private String mType = "";

    protected Data(String type) {
        mType = type;
    }

    // other abstract stuff
}

class UIDData extends Data {
    @Element(name = "UniqueID")
    private String mUID;

    public UIDData(String UID) {
        super("UID");
        mUID = UID;
    }
}