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Yup, that would make sense. Try popping up a JFrame to keep the program going.

I highly doubt it. You were probably just using an old .class file. Simply cleaning the project in eclipse would have probably done the trick, but you never followed my advice to delete the .class...

That's not an error, it's just a warning, and it's pretty self-explanatory. It should not affect runtime behavior at all.

The Swing Timer works fine. I ran that code, and it runs exactly how I'd expect- it prints "hello" once. Are you sure you're running this code? Try deleting any .class files, recompiling, and trying...