Triangles in Java

Overview

This Java console program lets the user choose how many rows of asterisks to print and select between two patterns: an increasing triangle (“Pine Tree”) or a decreasing triangle (“Tornado”). The program demonstrates nested loops and a switch statement, key control structures for iterative pattern generation.

Features

• User-defined number of rows (size of the pattern)
• Two selectable patterns:
  • Pine Tree – increasing asterisk rows
  • Tornado – decreasing asterisk rows
• Implements nested for loops for pattern generation
• Uses a switch statement for user choice handling
• Displays clean console output with spacing for readability
• Simple and beginner-friendly structure

Code Implementation

import java.util.Scanner;

public class Triangles {
    public static void main(String[] args) {
        try (Scanner input = new Scanner( System.in )) {
            int numAsterisks;
            int choice;
            System.out.println();
            System.out.print("Enter the maximum number of rows of asterisks to print: ");
            numAsterisks = input.nextInt();
            System.out.println();
            System.out.println("Choose a pattern:");
            System.out.println("1. Pine Tree");
            System.out.println("2. Tornado");
            System.out.println();
            System.out.print("Enter your choice: ");
            choice = input.nextInt();
            System.out.println();

            switch (choice) {
                case 1 -> {
                    for (int i = 1; i <= numAsterisks; i++) {
                        for (int j = 1; j <= i; j++) {
                            System.out.print("*");
                        }
                        System.out.println();
                    }
                }

                case 2 -> {
                    for (int i = numAsterisks; i >= 1; i--) {
                        for (int j = 1; j <= i; j++) {
                            System.out.print("*");
                        }
                        System.out.println();
                    }
                }
                default -> System.out.println("Invalid pattern choice. Please choose 1 or 2.");
            }
            System.out.println();
        } catch (Exception e) {
            System.err.println("Error reading input: " + e.getMessage());
        }
    }
}

Sample Output

Notes

• Designed for console execution in Java (no GUI); assumes valid integer input from the user
• Ideal for beginners learning loops and conditional branching
• Demonstrates incremental and decremental iteration logic
• Compatible with Java 17+

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