Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n² in spiral order.
For example,
Given n = 3,
You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
] 

Naive Way: Use what I write in Spiral Matrix. Key point is current row/column 's fill in length get minus by one every two steps.
I comment what each parameter represents. Easy to understand and good looking.

 public class Solution {  
   public int[][] generateMatrix(int n) {  
     int[][] m = new int[n][n];  
     int len = n; // current row/column 's fill in length  
     int index = 0; // direction controller  
     int number = 1; // increasing numbers  
     int x = 0, y = -1; // current position  
     // fill in the matrix  
     while(len > 0){  
       if(index%2==1) len--;  
       switch(index++%4){  
         case 0:  
           for(int i = 0;i < len;i++) m[x][++y] = number++;  
           break;  
         case 1:  
           for(int i = 0;i < len;i++) m[++x][y] = number++;  
           break;  
         case 2:  
           for(int i = 0;i < len;i++) m[x][--y] = number++;  
           break;  
         case 3:  
           for(int i = 0;i < len;i++) m[--x][y] = number++;  
           break;  
         default:  
         break;  
       }  
     }  
     return m;  
   }  
 }