Vector.toArray(object [] a) ?

[Younes Essouabni]

Hello all,
I have a Vector that I previously filled with String values coming from a String[][] array.
Now , I need to get back my String [][] array from the vector.
The method Vector.toArray(Object[] a) doesn't works and I don't knwo why.

public static String[][] getData(Vector vector)
{
String [][] rows=null;
Vector subVector=null;
rows= new String [vector.size()][];
System.out.println("Vectorsize"+vector.size());
for (int i=0; i<vector.size();i++)
{
  subVector=((Vector)(vector.elementAt(i)));
  System.out.println("Inner Vectorsize "+subVector.size());
  String [] columns= new String [subVector.size()];

//  for (int j=0;j<subVector.size();j++)//Uncomment this for loop.
//  {
//    columns[j]=subVector.elementAt(j).toString();
//  }
  columns=(String[])subVector.toArray(columns);//comment this line
//  subVector.copyInto(columns);
  rows[i]= columns;
        }

return rows;
}

This code will not work and will throw a java.lang.ArrayStoreException,
unless I uncomment the for loop and comment this line :columns=(String[])subVector.toArray(columns);
I don't understand why? Isn't it supposed to do the same?
If anybody has an idea, I would be glad to understand.
Thx in advance
[ April 03, 2003: Message edited by: Younes Essouabni ]

[Michael Morris]

Hi Younes,
You must be passing in a subvector that has some element other a String somewhere. I tried it both ways with this:

    public static void main(String[] args) {
        Vector vector = new Vector();
        Vector a = new Vector();
        a.add("A");
        Vector b = new Vector();
        b.add("B");
        b.add("C");
        Vector c = new Vector();
        c.add("D");
        c.add("E");
        c.add("F");
        vector.add(a);
        vector.add(b);
        vector.add(c);
        String[][] d = getData(vector);
        for (int i = 0; i < d.length; i++) {
            for (int j = 0; j < d[i].length; j++) {
                System.out.print(d[i][j] + " ");
            }
            System.out.println("");
        }
    }

And got this output both times:

Vectorsize3
Inner Vectorsize 1
Inner Vectorsize 2
Inner Vectorsize 3
A
B C
D E F

Michael Morris

[Weerawit Maneepongsawat]

   Object[] a = baseVector.toArray();
   for(int i = 0; i < a.length; i++) {
      Vector subVector = (Vector) baseVector.elementAt(i);
      a[i] = subVector.toArray();   
   }

may be like this..i holp this help.

[Younes Essouabni]

Thank you Michael, thank you Weerawit.
It sees that you were right, there isn't only string object.
That's the reason why this one works: columns[j]=subVector.elementAt(j).toString();
and this one doesn't works : columns[j]=(String) subVector.elementAt(j);
I thought that both were the same, but it is not. One is "translating" an object into a string, and the other is casting an object into a string, which is permitted as long as the object effectively contains a string.
Thank you for your help