Question

How can I get an array of elements in a ArrayList of HashMaps? I have an HashMap with url key on it. The value is a url address. Several HashMaps are stored in a ArrayList. What I want is an array with all url strings. I’m not happy with the solution I found because I think it could be extracted from ArrayList with some manipulation.

    // Hashmap for ListView        
    ArrayList<HashMap<String, String>> itemsList = new ArrayList<HashMap<String, String>>();

    // Creating JSON Parser instance
    JSONParser jParser = new JSONParser();
    jParser.execute(url); 

    try {
        JSONObject json = jParser.get();

        items = json.getJSONArray(TAG_ITEMS);
        //This is the solution that I want to optimize
        urls = new String[items.length()];

        // looping through All items
        for(int i = 0; i < items.length(); i++){
            JSONObject c = items.getJSONObject(i);

            // Storing each json item in variable
            String title = c.getString(TAG_TITLE);
            String description = c.getString(TAG_DESCRIPTION);
            String author = c.getString(TAG_AUTHOR);

            // Media is another JSONObject
            JSONObject m = c.getJSONObject(TAG_MEDIA);
            String url = m.getString(TAG_URL);

            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();

            // adding each child node to HashMap key => value
            map.put(TAG_TITLE, title);
            map.put(TAG_DESCRIPTION, description);
            map.put(TAG_AUTHOR, author);
            map.put(TAG_URL, url);

            // Solution
            urls[i] = url;

            // adding HashList to ArrayList
            itemsList.add(map);
        }
    } catch (JSONException e) {
        e.printStackTrace();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } catch (ExecutionException e) {
        e.printStackTrace();
    }

Answer 1

From what I can deduce from your question, it sounds like you’re trying to do the following

// Assuming previously declared and instantiated urls ArrayList with populated values in the nested HashMaps. 
ArrayList<HashMap<String, String>> urls;
// Create a new List using HashMap.values from urls.
List<String> urlList = new ArrayList<String>(urls.get(index).values());

urls.get(index).values() will return a Collection view of the values contained in the HashMap at the specified ArrayList index, which will be used to instantiate and populate a new ArrayList.

If you want to obtain all of the values within each of the nested HashMaps or urls, you can do so in a similar manner, but you will need to iterate through the entire urls ArrayList

for (HashMap<String, String> urlValues : urls) {
    urlList.addAll(urlValues.values());
}

P.S. Forgive my bad variable names!