ClassCastException, casting Integer to Double

Question

ArrayList marks = new ArrayList();
Double sum = 0.0;
sum = ((Double)marks.get(i));

Everytime I try to run my program, I get a ClassCastException th

Answer 1

2 things to understand here -

1) If you are casting Primitive interger to Primitive double . It works. e.g. It works fine.

int pri=12; System.out.println((double)pri);

2) if you try to Cast Integer object to Double object or vice - versa , It fails.

Integer a = 1; Double b = (double) a; // WRONG. Fails with class cast excptn

Solution -

Soln 1) Integer i = 1; Double b = new Double(i);
soln 2) Double d = 2.0; Integer x = d.intValue();