地图 <String, List<? extends AbstractType> &gt;

Question

I was looking all around Stack Overflow but I don't know if that's possible but here is my question:

I have two types A and B extending from AbstractType , then I want a Map with both type of object inside like this:

Map<String,List<? extends AbstractType>> map = new HashMap();
map.put("toto",new Arraylist<A>);
map.put("sacha",new Arraylist<B>);
List<A> a = (List<A>)map.get("toto");

I have a safety warning which is completely understandable, but that's the best way I found to make this work.

The only safety option I found was to have two distinct lists, but I would rather prefer a map to avoid multiple if case.

I hope someone will have an idea.

Answer 1

You can also use instanceof to always make sure that you don't get in some trouble. Here is an example, you can modify it as per your requirements:

Map<String,List<? extends AbstractType>> map = new HashMap<>();
        map.put("toto",new ArrayList<A>());
        map.put("sacha",new ArrayList<B>());

        List<? extends AbstractType> objList = (List<? extends AbstractType>) map.get("toto");
        List<A> a = null;
        List<B> b = null; 
        if(objList.size() > 0 && objList.get(0) instanceof A){
            a = (List<A>) objList;
        }else if (objList.size() > 0 && objList.get(0) instanceof B){
            b = (List<B>) objList;
        }

Hope this helps!