public void setup(CommonPage<?> parentPage) {
    ...
}

public abstract class NavBarComponent implements IsElement {

    @Templated(value = "navbar.html#navBtn")
    public static class NavBarItemComponent extends SimpleValueItemComponent<String> {...}
    ...
}
public class RepoNavBarComponent extends NavBarComponent {
     ...
}

public class UserNavBarComponent extends NavBarComponent {
     ...
}

public abstract class CommonPage<T extends ContentComponent> {
     ...
}

public class UserCommonPage<T extends ContentComponent> extends CommonPage<T>{
     ...
}

public class RepoCommonPage<T extends ContentComponent> extends CommonPage<T> {
     ...
}