Counting the number of references to certain type in ArrayList

Question

Let's say I've made the following.

ArrayList<Object> happylist = new ArrayList<Object>();
happylist.add("cat");
happylist.add(98);
...

And so on, adding different types of elements. What sort of method would help me count how many times there was a reference to certain type in my ArrayList?

Answer 1

You can use the getClass() method to determine some object's class.

Take a look at the documentation for Object.

Answer 2

It could easily be done counting the number of different types of reference in the list using reflections. I have coded the following method:

public Map<String, Integer> countReferences(List<Object> happyList) {
    Map<String, Integer> referenceCounter = new HashMap<>();

    for (Object object : happyList) {
        String className = object.getClass().getName();
        referenceCounter.put(className, referenceCounter.getOrDefault(className, 0) + 1);
    }
    return referenceCounter;
}

Basically, each class with difference name gives difference reference. By counting reference to each type, and storing them in map gives you what you are looking for.

But I am not quite sure the usefulness of such particular problems.