Cast HashMap with HashMap

Question

Why cast does not work in this case directly with

HashMap<String, Double> mapDouble = (HashMap<String, Integer>) mapInteger;

Is there an easier way than a loop ?

HashMap<String, Double> mapDouble;
for (Map.Entry<String,Integer> entry : mapInteger.entrySet()) {
    mapDouble.put(entry.getKey(), new Double(entry.getValue()) );
}

@SotiriosDelimanolis don't know exactly how it works internally, but I think that it's just a type modification when the modification is possible. — Ghilas BELHADJ, Oct 15 '15 at 15:55
Related: https://stackoverflow.com/questions/2745265/is-listdog-a-subclass-of-listanimal-why-arent-javas-generics-implicitly-p — assylias, Oct 15 '15 at 15:56

score 2 · Accepted Answer · answered Oct 15 '15 at 16:05

2

Sorry, but you need a loop! You have to go all the mapInteger to convert the values one by one.

answered Oct 15 '15 at 16:05

ersdiniz

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score 0 · Answer 2 · answered Oct 15 '15 at 15:55

0

You could not cast the hashmap.

entrySet() will give better performance approach.

answered Oct 15 '15 at 15:55

Siva Kumar

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score 0 · Answer 3 · answered Oct 15 '15 at 16:08

0

It would be easier to use Map<String, Number>.

Map<String, Number> map = new HashMap<>();
for (int i = 0; i < 100; i++) {
    map.put(Integer.toString(i), i);
}
map.forEach((k, v) -> System.out.println(k + " -> " + v.doubleValue()));

answered Oct 15 '15 at 16:08

Flown

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Cast HashMap with HashMap

3 Answers3