Enthuware

Map has a method named keySet(), which returns Set<K>.

1:
Properties extends Hashtable<Object, Object> (note the concrete generic type of Object), so all references to K, V declared in Hashtable<K, V> become Object, Object. Just saying that Properties extends Hashtable is not enough; It should be Hashtable<Object, Object>.

2:
Properties overrides keySet() (and a bunch of other methods) to explicitly return Set<Object> in its source code

Code: Select all

    @Override
    public Set<Object> keySet() {
        return Collections.synchronizedSet(map.keySet(), this);
    }

noeloo wrote: ↑

Wed Feb 17, 2021 2:23 pm

How is this _ used as a keyword? What is purpose of that?