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.");
            }

Side note: Why are you doing line.equalsIgnoreCase(">")? Since when > can be uppercase or lowercase? — Maroun
– Maroun, Commented May 18, 2013 at 17:25

Duncan Jones · Accepted Answer · 2013-05-18 17:25:29Z

3

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));

answered May 18, 2013 at 17:25

Duncan Jones

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5 Comments

Hovercraft Full Of Eels Over a year ago

Or just create a new ArrayList object. 1+

Eric Jablow Over a year ago

The OP never adds items to a new list anyway. He needs to populate it somehow. There are other stylistic problems: lists should be a List<List<String>>, for example.

NineNine Over a year ago

Yeah, i tried that, but List wouldn't work: The type List is not generic; it cannot be parameterized with arguments <String>

Eric Jablow Over a year ago

Huh? Are you using the right List? Make sure you haven't imported java.awt.List by mistake.

Hovercraft Full Of Eels Over a year ago

@9903286 yep, you were using the wrong List likely. You need to use java.util.List.

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