class BaseClass {
    //
}
 class SubClass extends BaseClass{
    //
}
 class Transformer{
    BaseClass base;
    public Transformer(BaseClass base){
        this.base = base;
    }
    public void transform(){
        //transforms the Object to a subtype-object
        // ???
        this.base = new SubClass(); //something like this (but not so!!!)
    }
}


 class Programm{
    private List<BaseClass> list1 = new ArrayList<>();
    private List<BaseClass> list2 = new ArrayList<>();
    private List<BaseClass> list3 = new ArrayList<>();
    //many more Lists
    private List<BaseClass> listn = new ArrayList<>();



    public void main() {
        BaseClass myObject = new BaseClass();
        list1.add(myObject);
        list2.add(myObject);
        list3.add(myObject);
        listn.add(myObject);

        Transformer transformer = new Transformer(myObject);
        transformer.transform();

        //required result
        // All Lists contain the transformed Object (from Type SubClass)
    }
}