CODEWITHSUNDEEP
javaobjectdictionarycasting
Greezer
Greezer

Reputation: 231

Cannot cast <Object, Map<Object, Object>> Map into more specific typed Map

I'm trying to cast a Map like this : 

Map<Integer, Map<String, String>> map = 
                 (HashMap<Integer, Map<String, String>>) pMap;

pMap is typed :

Map<Object, Map<Object, Object>> pMap

Unfortunately it doesn't work and I'm curious to know why, and also if it's possible to avoid the problem.

Upvotes: 0

Views: 212

Answers (3)

Greezer
Greezer

Reputation: 231

So, here is what I did to avoid this problem :

I typed my Map like this : 

Map<? super Object, ? super Object>

And it works, I can put whatever I want inside this Map. It can be :

Map<String, String>

or : 

Map<Integer, Map<String, String>>

etc. It's the more flexible way I found. The only constraint is to cast the Map when I operate on the map (through Iterator or with keySet).

Hope it could help someone.

Upvotes: 0

Tej Kiran
Tej Kiran

Reputation: 2238

I am not much familiar with generic class but can you try Map<?, Map> map after replacing Integer by ? It will case your Integer easily and as you wrote above that this key can be string too so I hope it will work for you.

Upvotes: 0

Keppil
Keppil

Reputation: 46209

This is because even though Integer is a subtype of Object, Map<Integer, Integer> is not a subtype of Map<Object, Object>.

You simply cannot cast it that way.

This is explained further in the Java Tutorials.

Upvotes: 3

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