convert ArrayList of String[] to String[][]

[Tom Henricksen]

I can create a ArrayList and convert to String[]. How do I convert an ArrayList of String[] to String [][]?

import java.util.ArrayList;
 
public class StringArrays {
    public static void main(String[] args) {
        String[] stringArray = null;
        String[][] stringArrayArray = null;
        ArrayList stringArrayArrayList = new ArrayList(5);
        for (int j = 0; j < 5; j++) {
            ArrayList stringArrayList = new ArrayList(5);
            stringArrayList.add("zero");
            stringArrayList.add("one");
            stringArrayList.add("two");
            stringArrayList.add("three");
            stringArrayList.add("four");
 
            stringArray = new String[5];
            stringArray = (String[]) stringArrayList.toArray(stringArray);
 
            for (int i = 0; i < stringArray.length; i++) {
                System.out.println(stringArray[i]);
            }
 
        }
        stringArrayArrayList.add(stringArray);
        // Conver list of String[] to String[][]?
        stringArrayArray = 
    }
}  

Thanks,
Tom

[Ernest Friedman-Hill]

Same way.

stringArrayArray = (String[][]) stringArrayArrayList.toArray(new String[stringArrayArrayList.size()][]);

When you allocate an array of arrays, you only have to specify the first dimension, as here.
[ September 01, 2005: Message edited by: Ernest Friedman-Hill ]

[Stan James]

And you can specify a size of 0. The List only cares about the types, not the size. I don't know if it's worth saving a few cycles to allocate a new list just for that argument.

import java.util.*;
public class Test
{
   public static void main(String[] args)
   {
      String[] array1 = new String[] { "one", "two" };
      String[] array2 = new String[] { "three", "four" };
 
      List list = new ArrayList();
      list.add(array1);
      list.add(array2);
 
      String[][] array3 = (String[][])list.toArray( new String[0][] );
 
      System.out.println(array3[0][0]);
      System.out.println(array3[0][1]);
      System.out.println(array3[1][0]);
      System.out.println(array3[1][1]);
   }
}

[Ernest Friedman-Hill]

Originally posted by Stan James:
I don't know if it's worth saving a few cycles to allocate a new list just for that argument.

Yeah. But both IDEA and Eclipse have a keyboard shortcut to automatically do out the whole thing, including allocating the right-sized array, and I've seen it so often that to me, at least, it feels like an idiom.

[Steve Morrow]

And you can specify a size of 0. The List only cares about the types, not the size.

There's more to it than just type. According to the contract of toArray(), it will use the array you pass, if the array is large enough.
[ September 01, 2005: Message edited by: Steve Morrow ]

[Stan James]

Ah, that makes passing the right size sound worth while!