Re: Generics headache

But of course!
Currently, we have something like (but only 'like'):

abstract class Parser<T> {
        public abstract AST parse(Scanner scanner) ;
        public abstract void doAfterEachMatch(T value) ;

}

abstract class InterceptableParser<T> extends Parser<T> {
        // there isn't actually any foo, but YKWIM
        // the actual code is a bit too complicated to reproduce
        public void foo(T value) {
                this.doAfterEachMatch(value) ;
        }
}

I would refactor to:

abstract class Parser {
        public abstract AST parse(Scanner scanner) ;
}

abstract class ActionAfterMatchParser<T> extends Parser {
        public abstract void doAfterEachMatch(T value) ;
}

abstract class InterceptableParser<T> implements ActionAfterMatchParser<T=
{
        public void foo(T value) {
                this.doAfterEachMatch(value) ;
        }
}

I'd also change the purely abstract classes to interfaces.