SixSidedStar

// original facebook post:
// https://www.facebook.com/groups/javaharikrishna/permalink/1596271237165097/

// JUnit test class:
// https://pastebin.com/zmdNaJ7k

// Related "Intersecting Triangles" classes:
// Implementation:
// https://pastebin.com/xjyyaBm0
// JUnit test classes:
// https://pastebin.com/iiUDpLZG
// https://pastebin.com/9CCBV1C9

public class SixSidedStar {

    public static void printSixSidedStar(final int n) {
        if (n > 0) {
            printTopLines(n);
            printHorizonalLineOfStars(n);
            printMiddleLines(n);
            printHorizonalLineOfStars(n);
            printBottomLines(n);
        } else if (n < 0) {
            throw new IllegalArgumentException("Argument value for 'n' must not be negative.");
        }
    }

    private static void printTopLines(final int n) {
        for (int line = 0; line < n; ++line) {
            printTopOrBottomLine(n, line);
        }
    }

    private static void printBottomLines(final int n) {
        for (int line = n - 1; line >= 0; --line) {
            printTopOrBottomLine(n, line);
        }
    }

    private static void printTopOrBottomLine(final int n, final int line) {
        System.out.print(spaces(n * 3 - line));
        final String triangleStars = triangleStars(line);
        System.out.print(triangleStars);
        System.out.println();
    }

    private static void printHorizonalLineOfStars(final int n) {
        final int numberOfStars = n * 3 + 1;
        System.out.println(spaces(numberOfStars * 2).replace("  ", "* ").trim());
    }

    private static void printMiddleLines(final int n) {
        final int boundry = n - 1;
        for (int offset = -boundry; offset <= boundry; ++ offset) {
            final int line = Math.abs(offset);

            final int leftIndent = n - line;
            System.out.print(spaces(leftIndent));
            final String triangleStars = triangleStars(line);
            System.out.print(triangleStars);
            System.out.print(spaces((n + leftIndent) * 2 - 1));
            System.out.println(triangleStars);
        }
    }

    private static String triangleStars(final int line) {
        if (line == 0) {
            return "*";
        } else {
            return "*" + spaces(line * 2 - 1) + "*";
        }
    }

    private static String spaces(final int count) {
        return new String(new char[count]).replace('\0', ' ');
    }

}