convert ArrayList<String> to String[][]

Question

I'm trying to convert and Arrayylist of type string to a 2d-array, String[][] using the following way

    ArrayList<String> arrayList = new ArrayList<String>(); 
    arrayList.add("report1");
    arrayList.add("report2");
    arrayList.add("report3");

    String[][] array = new String[arrayList.size()][];
    for (int i = 0; i < arrayList.size(); i++) {
        ArrayList<String> row = arrayList.get(i);
        array[i] = row.toArray(new String[row.size()]);
    }

resulting a compilation error at ArrayList<String> row = arrayList.get(i);

Need suggestions to resolve this or is there anyother way I can achieve the same

You can only get a one-dimensional arrayList. You have an ArrayList<String>, not ArrayList<ArrayList<String>>. — nanofarad
– nanofarad, Commented Jul 24, 2013 at 11:49
Are you trying to convert a single dimensional list into two dimensional String array? — Suji
– Suji, Commented Jul 24, 2013 at 11:51
yes, I'm trying to convert it to 2d String array necessarily. — Mango
– Mango, Commented Jul 24, 2013 at 11:54
maybe this can help you stackoverflow.com/questions/2146488/… — MaVRoSCy
– MaVRoSCy, Commented Jul 24, 2013 at 11:59
@Mango: without knowing your desired output it is impossible to answer. — jlordo
– jlordo, Commented Jul 24, 2013 at 12:00

nanofarad · Accepted Answer · 2013-07-24 11:50:48Z

0

You only have an ArrayList, not ArrayList>. The former is a dynamic array of strings and you can get String[] out of it.

Simply call

String[] myArray=arrayList.toArray(new String[0]);

No need to get the size down as it'll get the size automatically.

If you wanted to get a char[][] then do:

char[][] chars=new char[arrayList.size()][0]
int i=0;
for(String s:arrayList){
    chars[i]=s.toCharArray();
    i++;
}

Note that we're incrementing a counter in the loop. The enhanced for loop doesn't provide us a counter.

answered Jul 24, 2013 at 11:50

nanofarad

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4 Comments

MaVRoSCy Over a year ago

that is for 2D arrays?

nanofarad Over a year ago

@MaVRoSCy No, the OP doesn't even have a 2D array at hand. They only have a single arraylist of strings.

Mango Over a year ago

converting it to String[] wouldnot help me

nanofarad Over a year ago

@Mango I can't help you as Java is neither magic nor psychic. You don't have a 2-D arrayList so it can't be converted to a 2D array. f you did have a 2D array I'd need to know how you want to split rows.

Suji · Accepted Answer · 2013-07-24 12:06:54Z

    // TODO Auto-generated method stub
    ArrayList<String> arrayList = new ArrayList<String>(); 
    arrayList.add("report1");
    arrayList.add("report2");
    arrayList.add("report3");
    arrayList.add("report4");
    arrayList.add("report5");
    arrayList.add("report6");
    arrayList.add("report7");
    arrayList.add("report8");
    arrayList.add("report9");

    int rowSize = 3;



    String[][] array = new String[rowSize][];
    int rowIndex=0;

    ArrayList<String> tempList = new ArrayList<String>();
    for (int i = 0; i < arrayList.size(); i++) {

        tempList.add(arrayList.get(i));

        if(i>0 && ((i+1)%(rowSize))==0){

            array[rowIndex++] = tempList.toArray(new String[tempList.size()]);
            tempList = new ArrayList<String>();
        }
    }

    // prints the result array for varification

    for(int i=0;i<array.length;i++){
        System.out.println("\n\nRow : "+i+"\n");
        String[] innerArray = array[i];
        for(int j=0;j<innerArray.length;j++){
            System.out.print(innerArray[j]+" ");
        }
    }

Change the rowSise variable value as you desired.

M Abbas · Accepted Answer · 2013-07-24 12:11:20Z

0

arrayList.get(i) it will return String not a arraylist of string. so compiler will give casting error.

if you want to achieve your functionality you can do it as following

  String[][] array = new String[arrayList.size()][];
  for (int i = 0; i < arrayList.size(); i++) {
      ArrayList<String> row = new ArrayList<String>();
      row.add(arrayList.get(i));
      array[i] = row.toArray(new String[row.size()]);
  }

edited Jul 24, 2013 at 12:11

M Abbas

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answered Jul 24, 2013 at 11:58

Dipul Patel

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