**Question:**

Write a Program in Java to fill a square matrix of size ‘n*n” in a spiral fashion (from the inside) with natural numbers from 1 to n*n, taking ‘n’ as input.

For example: if n = 5, then n*n = 25, hence the array will be filled as given below.

**Note:** Don’t be confused as to how the filling will start from the center. Just treat the above program as (see the difference in the direction of the arrows):

So, you see, this question is nothing but the same circular matrix which we did earlier (**See:** Java Program to print Circular (Spiral) Matrix). The only change is that here the filling of numbers is from ‘n*n’ to 1 every time decreasing by one. In the earlier program it was from 1 to ‘n*n’ every time increasing by one.

So slight changes in our earlier program will result into this new spiral matrix. The changes will be:

- Start ‘k’ from ‘n*n’ and not 1
- Change the condition in while loop to while(k >= 1)
- Decrease the value of ‘k’ every time as ‘k- -‘

**Solution:**

/** * The class Circular_Matrix2 creates a Square Matrix of size n*n and fills it in a circular fashion * @author : www.javaforschool.com * @Program Type : BlueJ Program - Java */ import java.io.*; class Circular_Matrix2 { public static void main(String args[])throws IOException { BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); System.out.print("Enter the number of elements : "); int n=Integer.parseInt(br.readLine()); int A[][]=new int[n][n]; int k=n*n, c1=0, c2=n-1, r1=0, r2=n-1; while(k>=1) { for(int i=c1;i<=c2;i++) { A[r1][i]=k--; } for(int j=r1+1;j<=r2;j++) { A[j][c2]=k--; } for(int i=c2-1;i>=c1;i--) { A[r2][i]=k--; } for(int j=r2-1;j>=r1+1;j--) { A[j][c1]=k--; } c1++; c2--; r1++; r2--; } /* Printing the Circular matrix */ System.out.println("The Circular Matrix is:"); for(int i=0;i<n;i++) { for(int j=0;j<n;j++) { System.out.print(A[i][j]+ "\t"); } System.out.println(); } } }

**Output:**

Can I write programs in the practical examinations without using ‘static void main’?

Is it permissible to write programs that create objects graphically in BlueJ.

Yes it is permissible. But it is better to declare main() as static so that it be called without the need of any object. Why do you not want to use static?