Question

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.

Answer 1

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.