java从键盘输入一个整数(1~20)则以该数字为矩阵的大小,把1,2,3…n*n 的数字 ...

//BCCN,java
import java.io.*;
public class BCCN
{
    final static int N=21;
    public static int i,j,k,n,sum=1,s;
    public static int a[][]=new int[N][N];
    public static void main(String args[])throws IOException
    {
      
        String str;
        BufferedReader buf;
      
        buf=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Input n (1<=n&&n<=20):");
        str=buf.readLine();
        n=Integer.parseInt(str);
        fun(a,n);
    }
    static void fun(int a[][],int n)
    {
        s=n*n;
        for(i=1;i<=n;i++)
        {
            for(j=i,k=i;k<=n-i+1;k++)
            {
                a[j][k]=sum;
                sum++;
                if(sum>s)
                    break;
            }
            for(j=i+1,k=n-i+1;j<=n-i+1;j++)
            {
                a[j][k]=sum;
                sum++;
                if(sum>s)
                    break;
            }
            for(j=n-i+1,k=n-i;k>=i;k--)
            {
                a[j][k]=sum;
                sum++;
                if(sum>s)
                    break;
            }
            for(j=n-i,k=i;j>=i+1;j--)
            {
                a[j][k]=sum;
                sum++;
                if(sum>s)
                    break;
            }
        }
        for(j=1;j<=n;j++)
        {
            for(k=1;k<=n;k++)
                System.out.print(a[j][k]+"\t");
            System.out.print("\n");
        }
    }
}