Java Program to Print a Hollow Pyramid

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Introduction

A hollow pyramid is a pyramid-shaped structure in which only the boundary elements are printed, leaving the inner part empty. In this guide, we will walk through a Java program that prints a hollow pyramid of a given height using nested loops.

Problem Statement

Create a Java program that:

• Accepts the number of rows (height) for the pyramid.
• Prints a hollow pyramid using stars (*), with only the boundary elements visible.

Example:

• Input: 5
• Output:

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

Solution Steps

1. Take Input: Accept the number of rows (height) from the user.
2. Print the Hollow Pyramid: Use nested loops to print spaces and stars such that only boundary elements of the pyramid are printed, with the first and last row fully filled.
3. Display the Result: Print the pyramid on the console.

Java Program

// Java Program to Print a Hollow Pyramid
// Author: https://www.rameshfadatare.com/

import java.util.Scanner;

public class HollowPyramid {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Get the number of rows for the pyramid
        System.out.print("Enter the number of rows: ");
        int rows = scanner.nextInt();

        // Step 2: Loop through each row
        for (int i = 1; i <= rows; i++) {
            // Step 3: Print spaces for proper alignment
            for (int j = i; j < rows; j++) {
                System.out.print(" ");
            }

            // Step 4: Print stars and hollow spaces
            for (int k = 1; k <= (2 * i - 1); k++) {
                if (k == 1 || k == (2 * i - 1) || i == rows) {
                    System.out.print("*");  // Print star at the boundary or last row
                } else {
                    System.out.print(" ");  // Print space for hollow part
                }
            }

            // Move to the next line after printing each row
            System.out.println();
        }

        // Close the scanner
        scanner.close();
    }
}

Explanation

Step 1: Take Input

• The program asks the user for the number of rows (height) of the pyramid.

Step 2: Loop Through Each Row

• A for loop iterates from 1 to rows (the number of rows), where each iteration corresponds to one row of the pyramid.

Step 3: Print Spaces for Alignment

• For each row, a nested loop prints the appropriate number of spaces (rows - i) before printing stars. This ensures that the pyramid is centered.

Step 4: Print Stars and Hollow Spaces

• A second nested loop prints the stars and spaces in each row. The stars are printed at the beginning (k == 1), the end (k == (2 * i - 1)), and for the last row (i == rows). Spaces are printed for all other positions in the row to create the hollow effect.

Output Example

For an input of 5, the program outputs:

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

Example with Different Input

For an input of 3, the program outputs:

  *
 * *
*****

Conclusion

This Java program demonstrates how to print a hollow pyramid using nested loops. By controlling the placement of spaces and stars, the program is able to create a hollow pyramid pattern. This exercise helps in understanding how to manipulate loops and print complex patterns in Java programming.

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