ArrayList of HashMap elements to Array

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!

Answer 2

It looks like you are building a table. If you can add the Google Guava Library, you could just use the following:

Table<Integer, String, String> Table = HashedBasedTable.create()

See the JavaDoc:

http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Table.html