Avoiding Returning Wildcard Types

Question

I have a class with a collection of Wildcard Types that is a singleton, something like:

public ObliviousClass{

    private static final ObliviousClass INSTANCE          


        

Answer 1

Simply type your class:

public ObliviousClass  {

    private Map> map = new HashMap>();

    public void putType(Key key, Type type){
        map.put(type);
    }

    public Type getType(Key key){
        map.get(key);
    }
}

FYI, at this point you have the delegation pattern in play.

Your example client code would need to declare two instances of ObliviousClass: ObliviousClass and ObliviousClass.

Edit:

If you must have a mixed bag of Types, you can impose a type on your method, but you'll get a compiler warning for an unsafe cast:

public class ObliviousClass {

    private final Map> map = new HashMap>();

    public void putType(Key key, Type value) {
       map.put(key, value);
    }

    @SuppressWarnings("unchecked")
    public  Type getType1(Key key, Class typeClass) {
       return (Type)map.get(key); 
    }

    @SuppressWarnings("unchecked")
    public  Type getType2(Key key) {
        return (Type) map.get(key);
    }
}

Clients can type the calls to these methods like this:

Type x = obliviousClass.getType1(key, Integer.class);
Type y = obliviousClass.getType2(key);

Take your pick as to which one you prefer and use that.