Method Reference example in JLS

Question

JLS 15.13 lists examples of method reference expressions. One of them is

(test ? list.replaceAll(String::trim) : list) :: iterator

which doesn't make sense since replaceAll is void. Am I misunderstanding something or is this an error in JLS (perhaps an earlier version of replaceAll returned the resulting list)?

Answer 1

Well, technically it's not specified in JLS that the list variable has java.util.List type. So this code can be compiled with some custom type:

public static class MyList implements Iterable<String> {
    private final List<String> list = new ArrayList<>();

    public MyList add(String val) {
        list.add(val);
        return this;
    }

    public MyList replaceAll(UnaryOperator<String> op) {
        list.replaceAll(op);
        return this;
    }

    public Iterator<String> iterator() {
        return list.iterator();
    }
}

public Supplier<Iterator<String>> it(MyList list, boolean test) {
    return (test ? list.replaceAll(String::trim) : list) :: iterator;
}

But in general it looks like they intended to make an example based on java.util.List. Thus probably it would be best to replace it with something JDK-based.