public class Test2DArray {

  public static void main (String[] argv)
  {
    int size = 5;
    int[][] identMatrix;

    // Create the first dimension - an array
    identMatrix = new int[size][];

    // Create the second dimension - an array for each 
    // element of the first dimension.
    for (int i=0; i<size; i++)
      identMatrix[i] = new int[size];   // The size can be changed dynamically.

    // We're done creating the 2D array. Now create the
    // identity matrix and print it out.
    System.out.println ("Identity matrix of size: " + size);
    for (int i=0; i<size; i++) {
      for (int j=0; j<size; j++) {
        if (i == j) 
          identMatrix[i][j] = 1;
        else 
          identMatrix[i][j] = 0;
        System.out.print (identMatrix[i][j] + " ");
      }
      System.out.println ("");
    }
  }
}