Triangle Example in Java

Introduction

Triangle is a classic Java console program that demonstrates the concept with complete source code and sample output. Pattern programs print shapes with nested loops — common in exams and interviews.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Definition

A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry.

Triangle Example Program

class Triangle{
	public static void main(String[] args){
		for (int i = 0; i < 5; i++){
            for (int j = 5; j > i; j--){
                System.out.print(" ");
            }
            for (int k = 1; k <= i + 1; k++) {
                System.out.print(" *");
            }
        System.out.print("\n");
        }
	}
}

Sample Output

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

When to use

Use pattern logic when practicing nested loops or preparing for coding tests that ask for triangle or pyramid output.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. for (int i = 0; i < 5; i++){ updates a variable used in the calculation or output.

3. for (int j = 5; j > i; j--){ updates a variable used in the calculation or output.

4. A println / print call writes text to the console — part of the sample output below.

5. for (int k = 1; k <= i + 1; k++) { updates a variable used in the calculation or output.

6. A println / print call writes text to the console — part of the sample output below.

7. A println / print call writes text to the console — part of the sample output below.

8. Compare your console output with the sample output for Triangle to confirm the program behaves correctly.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.