Triangle Number Pattern in Java

Overview

This Java program generates a centered triangle pattern of numbers based on user input. The numbers in each row increase from 1 to the row index and then decrease back to 1. The pattern is aligned symmetrically using spaces for formatting.

Pattern Example

For n = 5, the output is:

    1
   121
  12321
 1234321
123454321

Code

package number_patterns;

import java.util.Scanner;

public class Triangle_Pattern
{
    public static void main(String[] args)
    {
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the size");
        int n = s.nextInt();
        
        for(int i = 1; i <= n; i++)
        {
            int num = 1;
            
            for(int j = i; j <= n; j++)
            {
                System.out.print(" ");
            }
            
            for(int j = 1; j < i; j++)
            {
                System.out.print(num++);
            }
            
            for(int j = 1; j <= i; j++)
            {
                System.out.print(num--);
            }
            
            System.out.println();
        }
    }
}

Explanation

1. Scanner Class

Scanner s = new Scanner(System.in);

• The Scanner class is used to take user input.
• System.in reads the input from the console.
• s.nextInt() retrieves an integer value entered by the user.

2. Variable Declaration

int n = s.nextInt();

• n stores the number of rows for the triangle pattern, entered by the user.

3. Outer For Loop (Row Control)

for(int i = 1; i <= n; i++)

• Controls the number of rows in the pattern.
• Runs from 1 to n, where n is the input number.

4. Printing Spaces (First Inner Loop)

for(int j = i; j <= n; j++)
{
    System.out.print(" ");
}

• Creates leading spaces to align the pattern centrally.
• The number of spaces decreases as i increases.

5. Printing Increasing Numbers (Second Inner Loop)

int num = 1;
for(int j = 1; j < i; j++)
{
    System.out.print(num++);
}

• Prints numbers increasing from 1 up to i-1.
• num++ increments num after printing.

6. Printing Decreasing Numbers (Third Inner Loop)

for(int j = 1; j <= i; j++)
{
    System.out.print(num--);
}

• Prints numbers decreasing from num back to 1.
• num-- decrements num after printing.

7. Printing a New Line

System.out.println();

• Moves to the next line after completing one row.

Summary

• The program generates a triangle pattern of numbers with symmetry.
• Uses nested loops to control spaces, increasing numbers, and decreasing numbers.
• Demonstrates fundamental Java concepts such as loops, conditionals, and user input handling.

Usage

1. Compile the program: javac Triangle_Pattern.java
2. Run the program: java Triangle_Pattern
3. Enter a number to define the pattern size.
4. Observe the structured triangle pattern in the console.

Clone

git clone https://github.com/Ananthadatta02/Java-Trainagle_Patterns.git