Adding Array elements to 2d ArrayList

Question

I'm having trouble adding array elements to an arraylist. I used some old code that I used to put array elements into a 2D array. However when I try to put a string array into my arraylist I get the following error: Array type expected; found: 'java.util.ArrayList<java.lang.String[]>'

I can't figure out how to cast the string into and arraylist object if that's the right thing to be doing?

You can see my code below:

 public void scoresArrayListMethod(){
        InputStreamReader InputSR = null;
        BufferedReader BufferedRdr = null;
        String thisLine = null;

        AssetManager am = getAssets();
        ArrayList<String []> alScores = new ArrayList<>();

        try {
            InputSR = new InputStreamReader(am.open("testdata/test_scores.txt"));
            BufferedRdr = new BufferedReader(InputSR);

            // open input stream test_scores for reading purpose.
            int i = 0;
            while ((thisLine = BufferedRdr.readLine()) != null) {


                String[] parts = thisLine.split(" ");

                alScores.addAll(parts); // Tried this with no joy
                alScores[i][1] = parts[1];  //Tried this with no joy
                alScores[i][2] = parts[2];

                i = i +1;
            }
            BufferedRdr.close();
            InputSR.close();

        } catch (Exception e) {
            e.printStackTrace();

        }

    }

Thanks,

Airfix

You're calling addAll(...) which expects another collection, but yet you're passing in an array. A look at the API would be a better first solution before coming here. Assuming you've done this, what was unclear about the add and addAll methods? — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Jul 14, 2016 at 0:08
And note that you don't have a "2d arraylist". You have an ArrayList of String arrays. That's a horse of a different color. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Jul 14, 2016 at 0:09
@Hovercraft The help file method states "Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices)." That's what I thought I was doing i.e. adding parts[1] to the ArrayList at position alScores[i][1]. — Airfix
– Airfix, Commented Jul 14, 2016 at 0:27

waynchi · Accepted Answer · 2016-07-14 00:22:13Z

1

addAll(...) adds the each element inside an Array into your ArrayList. So by using addAll you're adding Strings into your ArrayList rather than adding a String Array.

To fix this just change alScores.addAll(parts); to alScores.add(parts);

answered Jul 14, 2016 at 0:22

waynchi

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5 Comments

Airfix Over a year ago

Ahh I tried something similar to that but I was trying to add specific index locations from the array to the arraylist. I had tried 'alScores[i][1].add(parts[1]);'

waynchi Over a year ago

Does this mean you managed to fix it? :) If so then great. If not let us know.

Airfix Over a year ago

Not quite. I'm still working on it trying to return the values at various indices and making sure I can generate the full arraylist

Airfix Over a year ago

thanks for the constructive help. I was 90% there and I just needed that little push to get me over the hill. I've got my code working now. Thanks for the help. I used your alScores.add(parts); and System.out.println("the value of alScores [" + i + "][0] is " + alScores.get(i)[0]); to verify the ArrayList generates correctly.

waynchi Over a year ago

Glad I could help.

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