Casting Map<Integer, Set<Object>>

Question

I have a method that takes a Map<Integer, Set<Object>> as parameter. I need to call it from two different locations, using a Map<Integer, Set<String>> and a Map<Integer, Set<Integer>> as parameter.

The compiler complaint so I changed the method parameter signature to Map<Integer, ?>, and now I can call it, but have different problems. The method is basically as follows:

private void methodA (Map<Integer, ?> inOutMap, Integer key, Object value) {

        Set<Object> list = new HashSet<Object>();

        if (!inOutMap.containsKey(key)) {
            list.add(value);
        } else {
            list = (Set<Object>) (Set<?>) inOutMap.get(key); //I wrote the cast, but looks quite ugly
            list.add(value);
        }

        inOutMap.put(key, list); //compiler error
        //The method put(Integer, capture#4-of ?) in the type Map<Integer,capture#4-of ?> is not applicable for the arguments (Integer, Set<Object>)
    }

Is there any way of solving the compiler error? This is, casting list to ?.

My second question is conceptual. Is there any better way of doing this besides writting two different methods with different parameters signature?

Answer 1

declare it as

private <T> void methodA (Map<Integer, Set<T>> inOutMap, Integer key, T value) {

        Set<T> list = new HashSet<T>();

        if (!inOutMap.containsKey(key)) {
            list.add(value);
        } else {
            list = inOutMap.get(key); 
            list.add(value);
        }

        inOutMap.put(key, list); 
    }

Its always good to use Generics when you are trying to use multiple types of arguments, than using Object or ? (unknown type)

Now you can invoke the same method using Set containig different types like below

Map<Integer, Set<String>> m1 = new HashMap<Integer, Set<String>>();
Map<Integer, Set<Integer>> m2 = new HashMap<Integer, Set<Integer>>();

methodA(m1, 1, "t");
methodA(m2, 2, 2);

Answer 2

This compiles without errors and without explicit casting

private <T> void methodA (Map<Integer, Set<T>> inOutMap, Integer key, T value) {
    Set<T> list = new HashSet<T>();
    if (!inOutMap.containsKey(key)) {
        list.add(value);
    } else {
        list = inOutMap.get(key);
        list.add(value);
    }
    inOutMap.put(key, list);
}