The program displays first n*n natural numbers arranged in clockwise spiral in n*n array

spiral.java

/*
 * The program displays first n*n natural numbers arranged in clockwise spiral in n*n array
 *
 * Example:
 *
 * for n = 3; output
 *
 * 1 2 3
 * 8 9 4
 * 7 6 5
 *
 * Note: formatting for double digits isn't looked into
 *
 * @author Gaurav Narula
 *
 * */

public class spiral {
    private int[][] arr;
    private int n;

    public spiral(int n) {
        this.n = n;
        arr = new int[n][n];
    }

    public void magic() {
        int temp = n;
        int k = 0;
        int last = 0;
        int count = 0;

        while(count < n*n) {
            // fill the upper horizontal row

            for(int i = k; i < temp && count != n*n; i++, last++) {
                arr[k][i] = last + 1;
                count++;
            }

            // fill the right column

            for(int i = k; i < temp - 1 && count != n*n; i++, last++) {
                arr[i+1][temp-1] = last + 1;
                count++;
            }

            // fill lower horizontal row

            for(int i = temp - 2; i >= k && count != n*n; i--, last++) {
                arr[temp-1][i] = last + 1;
                count++;
            }

            // fill left column

            for(int i = temp - 2; i > k && count != n*n; i--, last++) {
                arr[i][k] = last + 1;
                count++;
            }

            temp -= 1;
            k++;
        }
    }

    public void display() {
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < n; j++)
                System.out.print(arr[i][j] + " ");
            System.out.println();
        }
    }

    public static void main(String[] args) {
        spiral ob = new spiral(7);
        ob.magic();
        ob.display();
    }
}