Question

Run time exception– java.lang.ClassCastingException…

Integer intArr[] = new Integer[arrList.size()];
ArrayList <Integer> arrList =new ArrayList();
intArr=(Integer[])arrList.toArray(); // returns Object class which is downcaste to Integer;

I understand down-casting is not safe but why is this happening?
I also tried to converting ArrayList to String to Integer to int, but I get the same error.

Answer 1

First of all, this doesn’t bind the ArrayList to type Integer.

ArrayList <Integer> arrList =new ArrayList();

Instead, this is what happens, arrList is assigned to an ArrayList of raw type, but that isn’t a problem.

The problem lies in,

intArr=(Integer[])arrList.toArray();

since arrList is a raw-type (due to the assignment, it gets assigned as new ArrayList<Object>() by the compiler), you’re effectively getting an Object[] instead.

Try assigning arrList to new ArrayList<Integer>() and do this:

intArr = arrList.toArray(new Integer[arrList.size()]);