How to retrieve List object stored in TreeMap?

Question

I have a list of objects that I needed to sort by category and also alphabetically. My idea was to take my ArrayList, convert it to a HashMap so that I could use a key to organize my data by category, and then createe a treemap to naturally alphabetize the data. It works, and I am not certain of a better/more efficient way of doing this. My TreeMap has the following structure:

TreeMap<String, ArrayList<CustomModel>>

How do I access the list of values from this treemap? I understand that I can get a specific value, if it were a String for example like the following:

for (Map.Entry<String, String> entry : treemap.entrySet()) {
            Log.i(TAG, "key= " + entry.getKey());
            Log.i(TAG, "value= " + entry.getValue());
        }

However, what if you have a list of values? How do I retrieve everything within that list? Seems like I need another conversion.

score 1 · Answer 1 · answered Apr 11 '18 at 20:03

1

It seems like you already have this solved. Entry.value() will return the ArrayList, instead of the String type. Try enumerating this and then logging each value

answered Apr 11 '18 at 20:03

user9594796

11
2

You are right, more or less. It does not return a list, it returns an object reference id. You have to use toArray() to get back the list. I included more details, but the work seems to be done and I accomplished what I wanted to accomplish which was sorting and alphabetizing – portfoliobuilder Apr 11 '18 at 21:39

portfoliobuilder · Answer 2 · 2018-04-11T21:44:30.773

I got the answer. There are a couple of ways of doing this. You can retrieve an object from your list, or the entire list object.

1) Object From List

You need a key to do this option. Get the key using keySet()

Object key = treemap.keySet().toArray()[index];
Object value = treemap.get(key);

2) Entire List Object

ArrayList<CustomModel> alCustomModel = (ArrayList<CustomModel>) treemap.values().toArray()[index];

Some notes about this, is that you are retrieving the list of CustomModels per position. Use whichever methodology makes sense to you. Cheers!

How to retrieve List object stored in TreeMap?

2 Answers2