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

Unchecked cast means that you are (implicitly or explicitly) casting from a generic type to a nonqualified type or the other way around. E.g. this line

Set<String> set = new HashSet();

will produce such a warning.

Usually there is a good reason for such warnings, so you should try to improve your code instead of suppressing the warning. Quote from Effective Java, 2nd Edition:

Eliminate every unchecked warning that you can. If you
eliminate all warnings, you are assured that your code is typesafe, which is a very
good thing. It means that you won’t get a ClassCastException at runtime, and it
increases your confidence that your program is behaving as you intended.

If you can’t eliminate a warning, and you can prove that the code that
provoked the warning is typesafe, then (and only then) suppress the warning
with an @SuppressWarnings("unchecked") annotation. If you suppress warnings
without first proving that the code is typesafe, you are only giving yourself a
false sense of security. The code may compile without emitting any warnings, but
it can still throw a ClassCastException at runtime. If, however, you ignore
unchecked warnings that you know to be safe (instead of suppressing them), you
won’t notice when a new warning crops up that represents a real problem. The
new warning will get lost amidst all the false alarms that you didn’t silence.

Of course, it is not always as easy to eliminate warnings as with the code above. Without seeing your code, there is no way to tell how to make it safe though.