Class Cast Exception

Question

why do i get this exception?

Map myHash = null myHash = (HashMap)Collections.synchronizedMap(new HashMap());

If i try to use this hashmap, i get java.lang.ClassCastException

Answer 1

Because Collections.synchronizedMap() does not return a HashMap.

Correct way should be:

Map mySyncedMap = Collections.synchronizedMap(new HashMap());

(or any other map instead of HashMap)

Answer 2

Because Collections.synchronizedMap does not return a HashMap.

It returns some other kind of Map (the type of which you should not need to know), that wraps your HashMap.

You have to use the Map interface instead of HashMap.