toArray() class cast exception

List<Record> recordsList = new ArrayList<Record>(2);

...

Record[] records = (Record[]) recordsList.toArray() ; //incorrect

Record[] records = (Record[]) recordsList.toArray(new Record[2]); //correct

Why Class cast exception ?

Recall that a Collection can contain objects of vastly different types. There's no 'general' rule that objects in a Collection must all be of the exact same type. So when toArray() is being calling, it allocates a typed array Object[] which has no sub-classes defined. Therefore casting it to any form such as (Record[]), will not work.

toArray() method can't see your cast so you have to tell it what kind of array to make.