Java Program to Print a Butterfly Pattern

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Introduction

A butterfly pattern is a fun and visually appealing pattern that can be printed using stars (*). The pattern is symmetrical, with the left and right wings of the butterfly expanding outwards, then shrinking back inwards. The butterfly pattern is a good exercise for learning how to use loops for pattern printing in Java.

Problem Statement

Create a Java program that:

• Accepts the size of the butterfly pattern.
• Prints the butterfly-shaped pattern using stars (*).

Example:

• Input: 5
• Output:

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

Solution Steps

1. Take Input: Define the size of the butterfly pattern.
2. Print the Upper Half: Use nested loops to print the upper half of the butterfly, expanding outwards.
3. Print the Lower Half: Use nested loops to print the lower half of the butterfly, shrinking back inwards.
4. Display the Result: Print the butterfly pattern on the console.

Java Program

// Java Program to Print a Butterfly Pattern
// Author: https://www.rameshfadatare.com/

import java.util.Scanner;

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

        // Step 1: Get the size of the butterfly pattern
        System.out.print("Enter the size of the butterfly pattern: ");
        int n = scanner.nextInt();

        // Step 2: Print the upper half of the butterfly pattern
        for (int i = 1; i <= n; i++) {
            // Step 3: Print the left wing of the butterfly
            for (int j = 1; j <= i; j++) {
                System.out.print("*");
            }

            // Step 4: Print spaces in the middle
            for (int j = 1; j <= 2 * (n - i); j++) {
                System.out.print(" ");
            }

            // Step 5: Print the right wing of the butterfly
            for (int j = 1; j <= i; j++) {
                System.out.print("*");
            }

            System.out.println();
        }

        // Step 6: Print the lower half of the butterfly pattern
        for (int i = n; i >= 1; i--) {
            // Step 7: Print the left wing of the butterfly
            for (int j = 1; j <= i; j++) {
                System.out.print("*");
            }

            // Step 8: Print spaces in the middle
            for (int j = 1; j <= 2 * (n - i); j++) {
                System.out.print(" ");
            }

            // Step 9: Print the right wing of the butterfly
            for (int j = 1; j <= i; j++) {
                System.out.print("*");
            }

            System.out.println();
        }

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

Explanation

Step 1: Take Input

• The program prompts the user for the size of the butterfly pattern. This size will determine the number of rows for the upper and lower halves of the butterfly.

Step 2-5: Print the Upper Half of the Butterfly

• The upper half of the butterfly is printed using a for loop that iterates from 1 to n (the number of rows).
• The first inner loop prints stars (*) on the left side of the butterfly.
• The second inner loop prints spaces (" ") in the middle of the butterfly.
• The third inner loop prints stars (*) on the right side of the butterfly.

Step 6-9: Print the Lower Half of the Butterfly

• The lower half of the butterfly is printed using a for loop that iterates from n down to 1.
• The process is similar to the upper half but in reverse, shrinking the number of stars as the rows move downward.

Output Example

For an input of 5, the program prints:

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

Example with Different Input

For an input of 4, the program outputs:

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

Conclusion

This Java program demonstrates how to print a butterfly-shaped star pattern using nested loops. The program is a great way to practice loop manipulation, pattern generation, and understanding symmetry in programming. By controlling the placement of stars and spaces, the program creates the butterfly shape efficiently.