Spiral matrix

Given the size of input n,print a spiral matrix of size n*n
ex: n=3

9 2 3
8 1 4
7 6 5

By observing the above matrix,we can construct the matrix by building first left column after bottom column after right column after top column.
code looks like below:

// program to print spiral matrix
 public static void getSpiralMatrix(int n) {
  int count = n * n;
  int[][] a = new int[n][n];
  // we have to construct a spiral matrix of size n*n
  for (int lower = 0, upper = n; lower <= upper; lower += 1, upper -= 1) {

   // first we fill the left side of the column
   for (int i = lower, j = lower; i < upper && count > 0; i++) {
    a[i][j] = count--;
   }

   // fill the lower row
   for (int i = upper - 1, j = lower + 1; j < upper - 1 && count > 0; j++) {
    a[i][j] = count--;
   }

   // fill the right side of the column
   for (int i = upper - 1, j = upper - 1; i >= lower && count > 0; i--) {
    a[i][j] = count--;
   }

   // fill the upper row
   for (int i = lower, j = upper - 2; j > lower && count > 0; j--) {
    a[i][j] = count--;
   }
  }
  for (int i = 0; i < n; i++) {
   for (int j = 0; j < n; j++) {
    System.out.print(a[i][j] + " ");
   }
   System.out.println();
  }
 }

Refer : http://www.geeksforgeeks.org/archives/10768