Filtering List objects by object type

Question

I have a List of Objects (ordered) which are already grouped by object type.

List<Object> myList = new ArrayList();
myList.add(new Integer());
myList.add(new Integer());
myList.add("string");
myList.add(new Double());
myList.add(new Double());
myList.add(new Double());

How can I elegantly loop through the groups of objects without using instanceof operator?

I essentially want this:

List<List<Object>> result;

I do not know what object types there are, so the simpleton approach would be to loop like this:

Object obj = iter.next();
String thisClass = obj.class.getSimpleName();
if (!thisClass.equals(lastClass)){
  currentList = new ArrayList();
}
currentList.add(obj);

however perhaps a stream would be nice, something like:

myList.stream().collect(Collectors.groupingBy(Class::getSimpleName, Collectors.<IBaseDO>toList()));

yes this results in a compile error as I can't get the syntax just right.

Ideas?

Answer 1

This is a very bad design.

Yet, you can do:

List<List<Object>> grouped = 
    myList.stream()
          .collect(collectingAndThen(
                       groupingBy(Object::getClass, LinkedHashMap::new, toList()), 
                       map -> new ArrayList<>(map.values)
          ));