[Patrick Chiang]

"X cannot be resolved as a type" errors are commonly caused by two reasons:
1. Missing import statement, wrong package.
2. Referring to a type that doesn't exist.

If you are using an IDE, there should be a way to automatically remedy this.

Also, doesn't Java make your implement all the methods of the abstract class?

    protected void execute() {
    }

    protected boolean isFinished() {
    }

    protected void end() {
    }

    protected void interrupted() {
    }