Converting a 2D List to a 2D array in Java

veryangryman · 01-08-2013 9:33am #1

Any budding geniuses help a brother out?

List<List<String>> allTestData = CliToolDataProvider.getAVCData();
String[][] result = allTestData.toArray(allTestData);

Javas toArray method seems to lack that 2 dimensional functionality. Any good way to rejig same to that the list of lists of strings can be converted to a simple 2D array.

Thanks in advance if you can help

Ri_Nollaig · 01-08-2013 9:59am

Just checked and it returns just a 1D array so thats not much use for you. So either some 3rd party library or write your own code:

This should work (not on a dev computer so can't test it)

List<List<String>> allTestData = CliToolDataProvider.getAVCData();
//String[][] result = allTestData.toArray(allTestData);

[COLOR="Red"]String[][] result = new String[allTestData.size()][];
for(int i = 0;i < allTestData.size();i++)
{
   List<String> testList = allTestData.get(i);
   String[] resultRow = new String[testList.size()];
   for(int j = 0;j < testList.size();j++)
   {
      resultRow[j] = testList.get(j);
   }
   result[i] = resultRow;
}[/COLOR]

enjoy

Aswerty · 01-08-2013 1:59pm

If you go with Ri Nollaigs approach you probably want to create a method called to2DArray() so it can easily be reused and doesn't clutter up your code.

Edit: Also you should use the existing .toArray() method in this approach so you don't need to implement the inner for loop.

onemorechance · 02-08-2013 4:35am

Obair baile? I think I remember this one from school!

I think you must declare the size of an array in Java before you can use it.

If this is the case, and you don't know how many items in your list(s), you may need to go through all the lists in the lists and find the one which has the highest count.

Converting a 2D List to a 2D array in Java

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