Problem of defender methods with generic methods

[Ali Ebrahimi]

Hi Maurizio,

when compiling the following code I get two error.

public interface CustomizedList<T> extends List<T> {
    extension CustomizedList<T> filter(Predicate<T> predicate) default
Trait.<T>filter;
    <R> extension CustomizedList<R> map(Extrator<T,R> predicate)
default Trait.<T,R>map;  <========== cannot find symbol R
    <A extends Comparable<? super A>> extension A max() default
Trait.<A>max;   <=============  cannot find symbol A

   public static class Trait {

        public  static <T> CustomizedList<T> filter(
                final CustomizedList<T> self, final Predicate<T> predicate) {
            CustomizedList<T> result=null;
            try {
                result = self.getClass().newInstance();
            } catch (Throwable e) {
                e.printStackTrace();
            }
            for(T elm:self){
                if(predicate.op(elm))
                    result.add(elm);
            }
            return result;
        }

        public static <T,R> CustomizedList<R> map(
                final CustomizedList<T> self, final Extrator<T,R> extrator) {
            CustomizedList<R> result=null;
            try {
                result = self.getClass().newInstance();
            } catch (Throwable e) {
                e.printStackTrace();
            }
            for(T elm:self){
                result.add(extrator.extract(elm));
            }
            return result;
        }

        public static <R extends Comparable<? super R>> R max(
                final CustomizedList<? extends R> self) {
            if(self.size()==0)
                return null;

            R result=self.get(0);
            for(R elm:self){
                if(elm.compareTo(result)>0)
                    result=elm;
            }
            return result;
        }
    }
}


Best Regards,

Ali Ebrahimi