Question

I have the below objects

interface Adapter<T> {
      T fromXml(XML xml);
      XML toXml(T obj); //ignoring this in implementations
}

abstract class AbstractAdapter<T> implements Adapter<T>{
       T fromXml(XML xml) { //template method
         validate(xml);
         return parse(xml);
       }
       abstract void validate(Xml xml);
       abstract T parse(Xml xml);
}

class MyObjectAdapter extends AbstractAdapter<MyObject> {
       MyObject parse(XMl xml) {return null;}
       void validate(Xml xml) {}
}

class AnotherObjectAdapter extends AbstractAdapter<AnotherObject> {
       AnotherObject parse(XMl xml) {return null;}
       void validate(Xml xml) {}
}

class AdapterFactory {
      Adapter<?> createAdapter(String objectType) {
         if (objectType == "MyObject") return new MyObjectAdapter();
         if (objectType == "AnotherObject") return new AnotherObjectAdapter();
}

public static void main(String args[]) {
      AdapterFactory factory = new AdapterFactory();
      //********
      Adapter<MyObject> myobjectAdapter = (Adapater<MyObject>) factory.createAdapter("MyObject");
      MyObject obj = myobjectAdapter.fromXml(getXml(args)); 
}

How do I avoid the downcasting I do in the line marked ** above?
The objects that need to have an adapter do not have any relation between them, they are generic data objects.

Answer 1

You have an class name in a String and you’re trying to go from that to the actual type. That is always going to involve a cast. If you remove the AdapterFactory and hence the String, then there is no problem.

(Usual note that == on Strings isn’t typically what you want.)