Hishigata.java

import java.util.Scanner;


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

        try {
            n = Integer.parseInt(args[0]);
        } catch (NumberFormatException e) {
            e.printStackTrace();
            System.exit(1);
        }

        if (n < 2) {
            System.out.println("Input Error : n >= 2 expected, but " + n);
            System.exit(1);
        }

        showDiamond(n);
    }

    private static void showDiamond(int n) {
        int center = n - 1;
        int cnt;
        for (int i = 0; i < 2 * n - 1; i++) {
            cnt = 0;
            for (int j = 0; j < n; j++) {
                if (Math.abs(i - center) > j)
                    System.out.print(" ");
                else {
                    System.out.print("*");
                    cnt++;
                }
            }

            for (int j = 0; j < cnt - 1; j++) {
                System.out.print("*");
            }

            System.out.println();
        }
    }
}

test_output.txt

=== input 2 ===
 *
***
 *
=== input 3 ===
  *
 ***
*****
 ***
  *
=== input 4 ===
   *
  ***
 *****
*******
 *****
  ***
   *
=== input 5 ===
    *
   ***
  *****
 *******
*********
 *******
  *****
   ***
    *
=== input 10 ===
         *
        ***
       *****
      *******
     *********
    ***********
   *************
  ***************
 *****************
*******************
 *****************
  ***************
   *************
    ***********
     *********
      *******
       *****
        ***
         *

testHishigata.sh

#!/bin/bash
set -eu

javac Hishigata.java

echo "=== input 2 ==="
java Hishigata 2

echo "=== input 3 ==="
java Hishigata 3

echo "=== input 4 ==="
java Hishigata 4

echo "=== input 5 ==="
java Hishigata 5

echo "=== input 10 ==="
java Hishigata 10