HollowOctagon.java

import java.util.Scanner;

public class HollowOctagon {

    public static void drawHorizontal(int leftAlign, char ch, int s) {
        for (int i=0; i<leftAlign; i++) {
            System.out.print(" ");
        } // for
        for (int i=0; i<s; i++) {
            System.out.print(ch);
        } // for
        System.out.println();
    } // drawHorizontal()

    public static void drawVerticals(int leftAlign, char ch, int s) {
        for (int i=0; i<s; i++) {
            for (int j=0; j<leftAlign-s+1; j++) {
                System.out.print(" ");
            } // for
            System.out.print(ch);
            for (int sp=0; sp<3*(s-1)-1; sp++) {
                System.out.print(" ");
            } // for sp
            System.out.println(ch);
        } // for i
    } // drawVerticals()

    public static void drawTopDiagonals(int leftAlign, char ch, int s) {
        for (int i=0; i<s-2; i++) {
            for (int j=0; j<leftAlign-(i+1); j++) {
                System.out.print(" ");
            } // for
            System.out.print(ch);
            for (int sp=0; sp<s+2*i; sp++) {
                System.out.print(" ");
            } // for sp
            System.out.println(ch);
        } // for i
    } // drawTopDiagonals()

    public static void drawLowerDiagonals(int leftAlign, char ch, int s) {
        for (int i=s-3; i>=0; i--) {
            for (int j=0; j<leftAlign-(i+1); j++) {
                System.out.print(" ");
            } // for
            System.out.print(ch);
            for (int sp=0; sp<s+2*i; sp++) {
                System.out.print(" ");
            } // for sp
            System.out.println(ch);
        } // for i
    } // drawLowerDiagonals()

    public static void main(String[] args) {
        char symbol = '*';
        int size = 10;
        int leftAlign = 10;

        Scanner scan = new Scanner(System.in);
        System.out.print("Enter size of octagon (up to 10): ");
        size = scan.nextInt();
        if (size>10) size=10;
        if (size<2) size = 2;

        System.out.println();

        drawHorizontal(leftAlign, symbol, size);
        drawTopDiagonals(leftAlign, symbol, size);
        drawVerticals(leftAlign, symbol, size);
        drawLowerDiagonals(leftAlign, symbol, size);
        drawHorizontal(leftAlign, symbol, size);
    } // main()

} // class HollowOctagon