fun key_set: HashSet[JavaString] import HashSet[JavaString],
	  HashSet[JavaString].add in "Java" `{
		Set<String> java_set = self.keySet();
		NitObject nit_hashset = new_HashSet_of_JavaString();

		for (String element: java_set)
			HashSet_of_JavaString_add(nit_hashset, element);

		return nit_hashset;
	`}