Iterate through an ArrayList of ArrayLists in Java

Question

I have the following ArrayList...

ArrayList<ArrayList<Integer>> row1 = new ArrayList<ArrayList<Integer>>();

The following arraylists are added to it....

row1.add(cell1);
row1.add(cell2);
row1.add(cell3);
row1.add(cell4);
row1.add(totalStockCell);

I want to iterate through the arraylist row1 and print the contents.

Would a loop within a loop work here?

E.g.

while(it.hasNext()) {

//loop on entire list of arraylists
    while(it2.hasNext) {
      //each cell print values in list

          } }

Adam Arold · Accepted Answer · 2013-12-09 12:30:03Z

5

This is the canonical way you do it:

for(List<Integer> innerList : row1) {
    for(Integer number : innerList) {
        System.out.println(number);
    }
}

answered Dec 9, 2013 at 12:30

Adam Arold

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Steve P. · Accepted Answer · 2013-12-09 12:30:00Z

2

for (ArrayList<Integer> list : row1)
{
    for (Integer num : list)
    {
        //doSomething
    }
}

Java enhanced-for loops use an iterator behind the scenes.

answered Dec 9, 2013 at 12:30

Steve P.

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Mehmet Sedat Güngör · Accepted Answer · 2013-12-09 12:34:51Z

0

If you want to use Iterator, nested loops will work:

    Iterator<ArrayList<Integer>> it = row1.iterator();

    while(it1.hasNext())
        {
        Iterator<Integer> itr = it.next().iterator();
        while(itr.hasNext())
            {
            System.out.println(itr.next());
            }
        }

answered Dec 9, 2013 at 12:34

Mehmet Sedat Güngör

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Ludov Dmitrii · Accepted Answer · 2019-07-27 18:19:07Z

0

Here some functional approach:

    ArrayList<ArrayList<Integer>> row1 = new ArrayList<>();
    row1.add(new ArrayList<>(Arrays.asList(1, 2, 3)));
    row1.add(new ArrayList<>(Arrays.asList(4, 5, 6)));
    row1.stream().flatMap(Collection::stream).forEach(System.out::println);

answered Jul 27, 2019 at 18:19

Ludov Dmitrii

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Tan-007 · Accepted Answer · 2019-08-16 17:30:08Z

0

Old question, but I am just curious why no one has mentioned this way,

for(int i=0; i<list.size(); i++) {          
    for(int j=0; j<list.get(i).size(); j++) {
        System.out.print(list.get(i).get(j) + " ");    
    }
    System.out.println();
}

This is same as accessing a matrix in 2D arrays.

edited Aug 16, 2019 at 17:30

answered Jul 27, 2019 at 18:01

Tan-007

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