Google guava iterables.filter, type errors related to generics?

Question

I have a custom predicate that has a signiture as follows:

public class ELPredicate<T> implements Predicate<T> 

I am attempting to filter them in a function similar to this:

public List<ComponentDefinition> filterComponents(String expression, List<ComponentDefinition> definitions) {

    if (definitions == null || definitions.size() == 0) {
        return new ArrayList<ComponentDefinition>();
    }

    ELPredicate<ComponentDefinition> predicate = new ELPredicate<>(expression);
    return Lists.newArrayList(Iterables.filter(definitions, predicate));
}

but i get this error:

The method filter(Iterable<T>, Predicate<? super T>) in the type Iterables is not applicable for the arguments (List<ComponentDefinition>, ELPredicate<ComponentDefinition>)

from what (I think) I know:

• Lists are iterable,
• <ComponentDefinition> is <? super ComponentDefinition>
• I am doing this in unit tests without any problem.

what's going on?

Answer 1

As it turns out, my problem was an access issue rather than a type issue. I was attempting to filter a private inner class (for testing purposes) and java apparently doesn't like that. I made it public and everything worked as expected.