How to print a Hollow Rhombus pattern in Java

How to print a Hollow Rhombus pattern in Java:

In this post, we will learn how to print a hollow Rhombus pattern with star in Java. I will show you how the algorithm works and how to write it in Java.

Algorithm to print a Rhombus:

A Rhombus of height 10 drawn with stars looks as below:

         * * * * * * * * * * 
        *                 * 
       *                 * 
      *                 * 
     *                 * 
    *                 * 
   *                 * 
  *                 * 
 *                 * 
* * * * * * * * * *

To understand how it works, let’s try it with a small Rhombus:

    * * * * * 
   *       * 
  *       * 
 *       * 
* * * * *

This is a Rhombus of height 5. We are using stars and blank spaces to print this pattern. Let me replace all blank spaces with #:

####* * * * * 
###* # # # * 
##* # # # * 
#* # # # * 
* * * * *

If you look closely,

On each row, it prints #, stars or # and stars.
We can run one for loop from i = 1 to i = height
- Inside this loop, run two for loops, the first one will print the starting blank spaces and the second one will print stars and blank spaces.
- The first inner loop will run from j = 1 to j = height - i. On each iteration, it will print a blank space.
- The second inner loop will run from k = 1 to k = height. If the value of i or k is 1 or height, it will print a star, else it will print a blank space on each iteration.

Example 1: Java program to print a hollow Rhombus with for loops:

The below Java program prints a hollow Rhombus pattern with user-input height value:

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the height of the Rhombus: ");

        int height = scanner.nextInt();

        for (int i = 1; i <= height; i++) {
            for (int j = 1; j <= height - i; j++) {
                System.out.print(" ");
            }
            for (int k = 1; k <= height; k++) {
                if (i == 1 || i == height || k == 1 || k == height) {
                    System.out.print("* ");
                } else {
                    System.out.print("  ");
                }
            }
            System.out.println();
        }
    }
}

It reads the height of the Rhombus and assigns it to the variable height. It is following the same algorithm we discussed above. You can run this program to print a Rhombus of any height.

Enter the height of the Rhombus: 
10
         * * * * * * * * * * 
        *                 * 
       *                 * 
      *                 * 
     *                 * 
    *                 * 
   *                 * 
  *                 * 
 *                 * 
* * * * * * * * * *

Example 2: Java program to print a hollow Rhombus with while loops:

We can re-write the above program with while loops. We have to initialize the variable before the loop starts and increment the value at the end of each iteration in the loop.

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the height of the Rhombus: ");

        int height = scanner.nextInt();
        int i = 1, j, k;

        while (i <= height) {
            j = 1;
            while (j <= height - i) {
                System.out.print(" ");
                j++;
            }

            k = 1;
            while (k <= height) {
                if (i == 1 || i == height || k == 1 || k == height) {
                    System.out.print("* ");
                } else {
                    System.out.print("  ");
                }
                k++;
            }
            System.out.println();
            i++;
        }
    }
}

This works exactly like the above program. You will get similar result.

Enter the height of the Rhombus: 
6
     * * * * * * 
    *         * 
   *         * 
  *         * 
 *         * 
* * * * * *

CodeVsColor

How to print a Hollow Rhombus pattern in Java