Clear properly a java arraylist

Question

I am trying to create a 2d ArrayList from a 2d array. Actually I ve got a temp ArrayListand I parse it to my 2d ArrayList in for loop. I am trying to find the correct way to clear this temp ArrayList in order to pass every time, the correct values to mags ArrayList.

   for (int m = 0; m < M; m++) {
        for (int n = 0; n < N; n++) {
            for (int i = 0; i < gaborWavelet.length; i++) {
                temp.clear();   
                for (int j = 0; j < gaborWavelet[0].length; j++) {
                    sum = gaborWavelet[i][j][m][n][0] / (M * N);
                    temp.add((int) (sum * 170));                
                }
                mags.add(temp);             
            }
        }
    }

In the above code only the final indexed-i it is passed in the temp m*n*i times.

EDIT:

        for (int m = 0; m < M; m++) {
        for (int n = 0; n < N; n++) {
            for (int i = 0; i < gaborWavelet.length; i++) {
                ArrayList<Integer> temp = new ArrayList<Integer>(); 
                for (int j = 0; j < gaborWavelet[0].length; j++) {
                    sum = gaborWavelet[i][j][m][n][0] / (M * N);
                    temp.add((int) (sum * 170));                
                }
                mags.add(temp);             
            }
        }
    }

    System.out.println(mags.get(200));
    System.out.println(mags.get(0));

If the above is what you mean, I am getting the same issue here.

Create an instance of your `temp` arrayList inside the `for(int i ..)` loop. On a different note, 4 nested loop!? — Some guy, Feb 06 '14 at 09:01
ArrayList.clear(). If that doesn't answer your question, what's your question? — user207421, Feb 06 '14 at 09:01
You don't want to clear temp list it in each loop. Instead create new lists for each "row" and add them to your `mags`. — Pshemo, Feb 06 '14 at 09:02

score 2 · Accepted Answer · edited May 23 '17 at 12:11

2

Instead of temp.clear() do temp = new ArrayList(). With your code in mags will be the same ArrayList added multiple times.

And read this post on how to create ArrayList from array

edited May 23 '17 at 12:11

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answered Feb 06 '14 at 09:05

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Clear properly a java arraylist

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