Java Generics -> Function return type

public interface FruitProducer<T> {
    T createFruit(String arg);
}

public <T> List<T> returnFruits(String arg, FruitProducer<? extends T> producer) {
    List<T> list = new ArrayList<T>();
    T fruit = producer.createFruit(arg);
    list.add(fruit);
    return list;
}

public abstract class FruitLister<T> {
    public abstract List<T> returnFruits(String arg);
}

public class AppleLister implements FruitLister<Apple> {
    @Override
    public List<Apple> returnFruits(String arg) {
            List<Apple> list = new ArrayList<Apple>();
            Apple apple = new Apple(arg);
            list.add(apple);
            return list;
    }
}