Get value (String) of ArrayList<ArrayList<String>>(); in Java

Question

I know it's simple question, but in

ArrayList<ArrayList<String>> collection;
ArrayList<String> listOfSomething;

collection= new ArrayList<ArrayList<String>>();
listOfSomething = new ArrayList<String>();

listOfSomething.Add("first");
listOfSomething.Add("second");
collection.Add(listOfSomething);
listOfSomething.Clear();
listOfSomething.Add("first");
collection.Add(listOfSomething);

I want to take String from ArrayList of ArrayList, and I don't know how to do that. For example I go

ArrayList<String> myList = collection.get(0); 
String s = myList.get(0);

and it works! but:

Big update:

private List<S> valuesS;
private List<Z> valuesZ;


ArrayList<ArrayList<String>> listOfS;
ArrayList<String> listOfZ;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
        Zdatasource = new ZDataSource(this);
        Zdatasource.open();
        valuesZ = Zdatasource.getAllZ();
        
        Sdatasource = new SDataSource(this);
        Sdatasource.open();
        valuesS = Sdatasource.getAllS();

        List<Map<String, String>> groupData 
             = new ArrayList<Map<String, String>>();
        List<List<Map<String, String>>> childData 
             = new ArrayList<List<Map<String, String>>>();

        listOfS = new ArrayList<ArrayList<String>>();
        listOfZ = new ArrayList<String>();
        for (S i : valuesS) { // S is class
            for (Z j : valuesZ) { // Z is class
                if(j.getNumerS().equals(i.getNumerS())) {
                    listOfZ.add(j.getNumerZ());
                }
                else
                {
                    //listOfZ.add("nothing");
                }
            }
                listOfS.add(listOfZ);
                if(!listOf.isEmpty()) listOfZ.clear();
        }



@Override
    public boolean onChildClick(ExpandableListView parent, View v, int groupPosition,
            int childPosition, long id) {
        try
        {       
            ArrayList<String> myList = listOfS.get(groupPosition); 
            String s = myList.get(childPosition);
         PrintToast("group "+Integer.toString(groupPosition)+", child "+Integer.toString(childPosition) + " , "+ s);
        }
        catch(Exception e)
        {
            Log.e("FS", e.toString());
        } 
        return true;
    }

return me java.lang.IndexOutOfBoundsException: Invalid index 1, size is 0 when I click on item which really should exist. I didn't show code which generate ListView, but I can tell you that my listOfS contains 3 items: first is Null listOfZ, second listOfZ got 2 elements, third listOfZ got 1 element.

If you got null, it means the second element of the first list in the collection is null. How could we help? — JB Nizet
– JB Nizet, Commented Apr 11, 2013 at 9:00

CloudyMarble · Accepted Answer · 2013-04-11 09:19:56Z

12

listOfSomething.Clear();
listOfSomething.Add("first");
collection.Add(listOfSomething);

You are clearing the list here and adding one element ("first"), the 1st reference of listOfSomething is updated as well sonce both reference the same object, so when you access the second element myList.get(1) (which does not exist anymore) you get the null.

Notice both collection.Add(listOfSomething); save two references to the same arraylist object.

You need to create two different instances for two elements:

ArrayList<ArrayList<String>> collection = new ArrayList<ArrayList<String>>();

ArrayList<String> listOfSomething1 = new ArrayList<String>();
listOfSomething1.Add("first");
listOfSomething1.Add("second");

ArrayList<String> listOfSomething2 = new ArrayList<String>();
listOfSomething2.Add("first");

collection.Add(listOfSomething1);    
collection.Add(listOfSomething2);

edited Apr 11, 2013 at 9:19

answered Apr 11, 2013 at 9:06

CloudyMarble

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1 Comment

boski Over a year ago

Yes. Correct. I use listOfZ = new ArrayList<String>(); instead of listOfZ.clear();

BobTheBuilder · Accepted Answer · 2013-04-11 09:06:42Z

11

Because the second element is null after you clear the list.

Use:

String s = myList.get(0);

And remember, index 0 is the first element.

answered Apr 11, 2013 at 9:06

BobTheBuilder

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1 Comment

boski Over a year ago

Yes that was true, but I write down example code and I make stupid mistake.

Nermeen · Accepted Answer · 2013-04-11 09:06:30Z

5

The right way to iterate on a list inside list is:

//iterate on the general list
for(int i = 0 ; i < collection.size() ; i++) {
    ArrayList<String> currentList = collection.get(i);
    //now iterate on the current list
    for (int j = 0; j < currentList.size(); j++) {
        String s = currentList.get(1);
    }
}

answered Apr 11, 2013 at 9:06

Nermeen

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Comments

user1897983 · Accepted Answer · 2013-04-11 09:12:04Z

5

A cleaner way of iterating the lists is:

// initialise the collection
collection = new ArrayList<ArrayList<String>>();
// iterate
for (ArrayList<String> innerList : collection) {
    for (String string : innerList) {
        // do stuff with string
    }
}

answered Apr 11, 2013 at 9:12

user1897983

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MEGHA RAMOLIYA · Accepted Answer · 2021-08-03 11:48:08Z

0

I have String array like this
We have to pass data through response.body.getdata and this data pass in constructor like this,

List taginnerData;

 "data": [
                "banana",
                "apple",
                "grapes",
                "Pears",
                "Mango",
                "Cherry",
                "Guava",
                "TorontoVsMilwaukee_12Jan19"
            ]

 String[] myArray = new String[taginnerData.size()];
        for (int i = 0; i < taginnerData.size(); i++) {
            myArray[i] = String.valueOf(taginnerData.get(i));
            holder.tv_channel_name.setText("" +taginnerData.get(i));
//we get any value from here to set in adapter
        }

answered Aug 3, 2021 at 11:48

MEGHA RAMOLIYA

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