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.
Try to do this
intArr = arrList.toArray(new Integer[arrList.size()]);
What you get is a typed Integer Array and not a Object array.
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()]);
List<Integer> arrList = new ArrayList<Integer>(); Integer[] ints = arrList.toArray(new Integer[arrList.size()]);.List<T>.toArray(T[] array);. Because I've said that arrList is type Integer, the toArray method expects and Integer array (at compile-time). The implementation returns all internal values of the list to an array. In other words, the Generic type T is bounded to an Object Integer. Study Generics.The problem here is that you are trying to convert an array of objects to an array of integers. Array is an object in itself and Integer[] is not a sub-class of ArrayList, nor vice versa. What you have to do in your case is cast individual items, something like this:
Integer intArr[] = new Integer[arrList.size()];
for(int i=0; i<intArr.length; i++)
{
intArr[i] = (Integer)arrList.get(i);
}
Naturally, you may get ClassCastException if individual elements in the array list are not of type Integer.
toArray(T[] a) takes a paramter:
"a - the array into which the elements of the list are to be stored, if it is big enough; otherwise, a new array of the same runt"
ArrayList<int>cannot be done. In other words, Generics cannot be applied on primitive types.Integer[]toint[].