How to dynamically store data in Multi Dimensional String Array

Question

I have a problem related to storing data dynamically in two Dimensional String Array, String[][]. I am dynamically storing data in the String[i][j] array. Here the first index's value is fixed i.e. i=3, but second index's value is different for all rows.

for example, I am getting values like this,

String arrElements[][] = {
        {"1"},
        {"abc", "xyz", "lkm", "pwd", "srt", "qwert"},
        {"1234", "3456"}
        };

I am getting values something like this. i.e there is only 1 value in the first row, any number of values in the second row and in the third row.

If I go like this,

    int i = 0, j = 0;
    String arrElements[][] = {};
    arrElements= new String[3][25];
            //What size should I define here.
    arrElements[0][0] = "Sahil";
    if (a == 0) { //Its just a logical representation of what I might be doing.
        // Store the value in second row
        arrElements[1][i] = a;
        i++;
    }
    if (a == 1) {
        // Store the value in third row
        arrElements[2][j] = a;
        j++;
    }

Now, I am setting these values in the expandable list View. If the number of values in any of the rows exceeds the size specified, it gives ArrayOutOfBoundException. and if the size is less than 25, it shows empty rows.

Now, I dont want to give hard coded size limit for the array indexes. Is there any better way to deal with it.

Stephan · Accepted Answer · 2013-01-17 08:29:08Z

1

As a first remark: Are you sure a String[][] is the right data structure for what you want to achieve? There is a whole bunch of Collection classes that might be more suitable (ArrayList to name the most obvious).

If you really want to proceed with String[][] you can't define the length of the sub-arrays upfront but have to declare it per row:

String[][] foo = new String[4][];
foo[0] = new String[1];
foo[1] = new String[2];
// ....

But as I said you might be much happier with a nested ArrayList which resizes dynamically:

ArrayList<ArrayList<String>> foo = new ArrayList<ArrayList<String>>();
// Do the following for each row
foo.add(new ArrayList<String>>());
// Do the following to append data in row i
foo.get(i).add("new string");
// Do the following to retrieve column j in row i
foo.get(i).get(j);

Depending on what you actually want to store, other data structures might be much more suited.

answered Jan 17, 2013 at 8:29

Stephan

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Sahil Mahajan Mj Over a year ago

First option sounds interesting. It would be good, if I could calculate the column count for each row and then define the length of sub-arrays.

dokkaebi · Accepted Answer · 2013-01-17 08:32:05Z

1

You can use whatever data structures you like.

In the ExpandableListAdapter that you pass to the view, just be sure you return correct values from getGroupCount and getChildrenCount. In getGroup and getChild, return the appropriate data from whatever backing structure you use (database cursor, list, list of lists, etc.).

One useful structure for this type of list is a Map<GroupData, List<ChildData>>. This might be as simple as a HashMap<String, ArrayList<String>> if the item text is the only data you have.

edited Jan 17, 2013 at 8:32

answered Jan 17, 2013 at 8:24

dokkaebi

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1 Comment

Sahil Mahajan Mj Over a year ago

Yes, I was also thinking about it. Could ArrayList be a good alternate for it.?

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