java - What is unchecked cast and how do I check it?

Question

I think I get what unchecked cast means (casting from one to another of a different type), but what does it mean to "Check" the cast? How can I check the cast so that I can avoid this warning in Eclipse?

Answer 1

To elaborate on what Peter wrote:

Casts from non-generic types to generic types may work just fine at runtime, because the generic parameters are erased during compilation, so we are left with a legitimate cast. However, the code may fail later with an unexpected ClassCastException due to an incorrect assumption regarding the type parameter. For example:

    List l1 = new ArrayList();
    l1.add(33);
    List<String> l2 = (List<String>) l1;
    String s = l2.get(0);

The unchecked warning at line 3 indicates that the compiler is not able to guarantee type safety, in the sense that an unexpected ClassCastException may occur at a later point. Indeed, this happens at line 4, which performs an implicit cast.