Adding list to a list of lists doesn't work

Question

I can not get this code to work. The .txt file that it is reading from is here: urls.txt

The problem with this code is that it does not at all add any lines. Whenever i try to get anything at all from "lists" it gives me an IndexOutOfBoundsException.

The code gets executed each 30 seconds, so i have to call the lists.clear(); method.

NOTE: "lists" is defined earlier:

    public static ArrayList<ArrayList<String>> lists = new ArrayList<ArrayList<String>>();

This is my code:

                try {
                URL urls = new URL("https://dl.dropboxusercontent.com/u/22001728/server%20creator/urls.txt");
                BufferedReader br = new BufferedReader(new InputStreamReader(urls.openStream()));

                lists.clear();

                String line;
                ArrayList<String> list = new ArrayList<String>();

                lists.add(list);

                int y = 0, z = 0;

                while ((line = br.readLine()) != null) {
                    y++;
                    if(line.equalsIgnoreCase(">")) {
                        System.out.print("Received command: INSERT ");
                        lists.add(list);
                        list.clear();
                        z++;
                        System.out.print(" ;  Jumping to " + z + "\n");
                    } else {
                        System.out.println("Line: " + line + " added to lists[" + z + "].");
                        lists.get(z).add(line);
                    }
                }

                int selectedIndex = comboModel0.getIndexOf(comboModel0.getSelectedItem());
                comboModel0.removeAllElements();

                System.out.println("\n\n\n");

                System.out.println(lists.get(1).get(1));

                System.out.println("\n\n\n");

            } catch (IOException e) {
                System.out.println("Failed to download URLS data.");
            }

Answer 1

You are adding a list to your collection of lists, then clearing it. That will clear your local variable, plus the list in your collection.

lists.add(list);
list.clear();

You need to create a copy of that list to add to your collection.

lists.add(new ArrayList<String>(list));