test_output.txt

compile ...
=== input 3 ===
***
* *
* *
=== input 4 ===
****
*  *
*  *
* **
=== input 5 ===
*****
*   *
* * *
* * *
* ***
=== input 6 ===
******
*    *
* ** *
* *  *
* *  *
* ****
=== input 7 ===
*******
*     *
* *** *
* * * *
* * * *
* *   *
* *****
=== input 8 ===
********
*      *
* **** *
* *  * *
* *  * *
* * ** *
* *    *
* ******
=== input 9 ===
*********
*       *
* ***** *
* *   * *
* * * * *
* * * * *
* * *** *
* *     *
* *******
=== input 10 ===
**********
*        *
* ****** *
* *    * *
* * ** * *
* * *  * *
* * *  * *
* * **** *
* *      *
* ********
=== input 11 ===
***********
*         *
* ******* *
* *     * *
* * *** * *
* * * * * *
* * * * * *
* * *   * *
* * ***** *
* *       *
* *********
=== input 12 ===
************
*          *
* ******** *
* *      * *
* * **** * *
* * *  * * *
* * *  * * *
* * * ** * *
* * *    * *
* * ****** *
* *        *
* **********
=== input 13 ===
*************
*           *
* ********* *
* *       * *
* * ***** * *
* * *   * * *
* * * * * * *
* * * * * * *
* * * *** * *
* * *     * *
* * ******* *
* *         *
* ***********
=== input 14 ===
**************
*            *
* ********** *
* *        * *
* * ****** * *
* * *    * * *
* * * ** * * *
* * * *  * * *
* * * *  * * *
* * * **** * *
* * *      * *
* * ******** *
* *          *
* ************
=== input 15 ===
***************
*             *
* *********** *
* *         * *
* * ******* * *
* * *     * * *
* * * *** * * *
* * * * * * * *
* * * * * * * *
* * * *   * * *
* * * ***** * *
* * *       * *
* * ********* *
* *           *
* *************
=== input 16 ===
****************
*              *
* ************ *
* *          * *
* * ******** * *
* * *      * * *
* * * **** * * *
* * * *  * * * *
* * * *  * * * *
* * * * ** * * *
* * * *    * * *
* * * ****** * *
* * *        * *
* * ********** *
* *            *
* **************
Done!

testUzumaki.sh

#!/bin/bash

set -eu

echo "compile ..."
javac Uzumaki.java

for i in {3..16}; do
    echo "=== input $i ==="
    java Uzumaki $i
done

echo "Done!"

Uzumaki.java

class Uzumaki {
    public static void main(String[] args) {
        int n = 0;

        try {
            n = Integer.parseInt(args[0]);
        } catch (NumberFormatException e) {
            System.err.println("Input Error : must be integer");
            System.exit(1);
        }

        if (n < 3) {
            System.err.println("Input Error : n >= 3 expected, but " + n);
            System.exit(1);
        }

        Uzu uzu = new Uzu(n);
        uzu.print();
    }

}

class Uzu {
    private int[][] uzu;
    private int pos_x;
    private int pos_y;
    private int length;
    private int cnt;

    Uzu (int length) {
        this.length = length;
        uzu = new int[length][length];
        pos_x = 0;
        pos_y = length - 1;
        uzu[pos_y][pos_x] = 1;
        cnt = 0;

        moveUp();

        if (length % 2 == 0)
            uzu[pos_y][pos_x] = 0;
    }

    private void moveUp() {
        if (pos_y > 0)
            if (uzu[pos_y-1][pos_x] == 1)
                return;

        if (pos_y > cnt) {
            pos_y -= 1;
            uzu[pos_y][pos_x] = 1;
            moveUp();
        } else
            moveRight();
    }

    private void moveRight() {
        if (pos_x < length - 1)
            if (uzu[pos_y][pos_x+1] == 1)
                return;

        if (pos_x < length - cnt - 1) {
            pos_x += 1;
            uzu[pos_y][pos_x] = 1;
            moveRight();
        } else
            moveDown();
    }

    private void moveDown() {
        if (pos_y < length - 1)
            if (uzu[pos_y+1][pos_x] == 1)
                return;

        if (pos_y < length - cnt - 1) {
            pos_y += 1;
            uzu[pos_y][pos_x] = 1;
            moveDown();
        } else
            moveLeft();
    }

    private void moveLeft() {
        if (pos_x > 0)
            if (uzu[pos_y][pos_x-1] == 1)
                return;

        // counting
        if (pos_x == cnt + 2 && pos_y == length - cnt - 1)
            cnt += 2;

        if (pos_x > cnt) {
            pos_x -= 1;
            uzu[pos_y][pos_x] = 1;
            moveLeft();
        } else
            moveUp();
    }

    public void print() {
        for (int i = 0; i < length; i++) {
            for (int j = 0; j < length; j++) {
                if (uzu[i][j] == 1)
                    System.out.print("*");
                else
                    System.out.print(" ");
            }
            System.out.println();
        }
    }
}