What is stopping me to make treetsByAuthor a method in Treet.java

Nothing is stopping you from making it a method; it even is a good idea in my opinion.

The only gotcha is that you must make it a static method and pass in the treets as an argument. This is because treetsByAuthor() must know about all the treets, not just one instance of a treet.

Here is my example for getHashTagCounts() that I made into a static method in Treet.java. You can try to follow the same pattern for treetsByAuthor():

    public static Map<String, Integer> getHashTagCounts(List<Treet> treets) {
        Map<String, Integer> hashTagCounts = new TreeMap<>();

        for (Treet treet : treets) {
            for (String hashTag : treet.getHashTags()) {
                hashTagCounts.putIfAbsent(hashTag, 0);
                hashTagCounts.put(hashTag, hashTagCounts.get(hashTag) + 1);
            }
        }

        return hashTagCounts;
    }

The only downside is that the Treet class is starting to gather many different responsibilities, potentially violating the Single Responsibility Pattern. So it might be even better from an Object-oriented Design standpoint to move the method into a separate class that deals with a collection of Treets. It could be called Treets.java (plural), TreetList.java, TreetCollection.java, TwitterTimeline.java, … (you get the idea).

Hi,

Can you share your code that's not working?

Steve.