Adding integer arraylist to arraylist in android

Question

I need to make a 2D arraylist like

[[1,2,3],[2,3,4],[3,4,5]]

But by using the below code I am getting only

[[3,4,5],[3,4,5],[3,4,5]]

The last array simply gets repeated again and again. While traversing through the problem, I found that in first pass its like

[[1,2,3]

2nd pass:

[[2,3,4],[2,3,4]]

3rd pass:

[[3,4,5],[3,4,5],[3,4,5]].

Please help, as i m stuck with it.

ArrayList<ArrayList<Integer>> combiarray = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> innerarray = new ArrayList<Integer>();

combiarray.clear();

for(k=1;k<(row*column);k=k+column)
{
    for(j=k;;j++)
        {
            innerarray.clear();
            for(i=0;i<wincount;i++)
            {
                innerarray.add(j+i);
            }

            combiarray.add(innerarray);
            Toast.makeText(context,String.valueOf(combiarray),
                                 Toast.LENGTH_SHORT).show();
            i--;
            if((j+i)%column==0)
            {
                break;
            }
        }
    }

Alexis C. · Accepted Answer · 2014-02-21 14:05:04Z

1

The problem is that you're always adding the same arraylist object to the list and you just modify its content. You have to create a new object at each iteration.

Currently you're doing something like this:

enter image description here

So replace

innerarray.clear();

by

innerarray = new ArrayList<Integer>();

edited Feb 21, 2014 at 14:05

answered Feb 21, 2014 at 13:57

Alexis C.

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Comments

Slimu · Accepted Answer · 2014-02-21 14:12:07Z

1

ArrayList class has a method called addAll that adds all the content from a collection to your collection. You can use it to add to your final ArrayList the content of the other lists.

If you wish to generate the lists in the required format, you can use:

 ArrayList<ArrayList<Integer>> combiArray = new ArrayList<ArrayList<Integer>>();
    int columns = 3;
    for (int i = 1; i <= columns; i++) {
        ArrayList<Integer> innerArray = new ArrayList<Integer>();
        for (int j = i; j < i + columns; j++) {
            innerArray.add(j);
        }
        combiArray.add(innerArray);
    }

edited Feb 21, 2014 at 14:12

answered Feb 21, 2014 at 13:54

Slimu

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3 Comments

Slimu Over a year ago

If he wants to add an ArrayList<Integer> to the ArraysList<ArrayList<Integer>>, just use add() method.

user3337408 Over a year ago

I used the add method. But it overwrites the old values in the arraylist.

Slimu Over a year ago

He was adding the same ArrayList instance to the combiarray, so of course it's values would be reset to the latest. Putting the innerArray in the loop makes that after each iteration, a new instance is created.

Anil kumar · Accepted Answer · 2014-02-21 13:58:16Z

0

try this once...

for(k=1;k<(row*column);k=k+column)
{
for(j=1;j<=k;j++)
    {
        innerarray.clear();
        for(i=0;i<wincount;i++)
        {
            innerarray.add(j+i);
        }

        combiarray.add(innerarray);
        Toast.makeText(context,String.valueOf(combiarray),Toast.LENGTH_SHORT).show();
        i--;
        if((j+i)%column==0)
        {
            break;
        }

    }
}

answered Feb 21, 2014 at 13:58

Anil kumar

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