从外向内扩的螺旋矩阵

public class SpiralMatrix {

    private int[][] data;
    private int n;
    
    public SpiralMatrix(int n)
    {
        if (n>=1)
        {
            this.n = n;
            data = new int[n][n];
            assignData();
        }    
    }
    
    public void assignData()
    {
        int m=1,i,j;
        for (i=0; i< n/2; i++)
        {
            for (j=0; j< n-i; j++)
            {
                if (data[i][j] == 0)
                    data[i][j] = m++;
            }
            
            for (j=i+1; j< n-i; j++)
            {
                if (data[j][n-1-i] == 0)
                    data[j][n-1-i] = m++;
            }
            
            for (j=n-i-1; j>i; j--)
            {
                if (data[n-i-1][j] == 0)
                    data[n-i-1][j] = m++;
            }
            
            for (j=n-i-1; j>i; j--)
            {
                if (data[j][i] == 0)
                    data[j][i] = m++;
            }
        }
        if (n%2 == 1)
            data[n/2][n/2] = m;
    }
    
    public void printData()
    {
        for (int i=0; i<n; i++)
        {
            for (int j=0; j<n; j++)
                System.out.print(data[i][j]+"\t");
            System.out.println();
        }
    }
    
    public static void main(String[] args)
    {
        SpiralMatrix  sm = new SpiralMatrix(7);
        sm.printData();
    }
    
}