How to get rid of this unchecked cast warning?

Question

Vector<Integer> v1 = new Vector<Integer>(); // ok
Object obj = (Object) v1; // ok
Vector<Integer> v2 = (Vector<Integer>) obj; //unchecked cast
It works when I try to cast Vector<Integer> to Object. However, it prompts "unchecked cast warning" when I try to cast the object back to Vector<Integer>. How can I get rid of this warning? Is there something wrong?

Answer 1

There is nothing wrong (it is just a warning).
In the new type system, you would later do something like
Integer n = v2.get(14);Now the compiler cannot check (compile time maybe, run time never) whether obj is of class Vector<Integer> (Only Vector), as at compile time as type parameters are stripped away in java1.5 at run time ("type erasure").
So later the assignment to n could throw a class cast exception at run time.