Pascal Triangle Example in Java

Introduction

Pascal 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

Pascal’s triangle is a triangular array of the binomial coefficients. The rows of Pascal’s triangle (sequence A007318 in OEIS) are conventionally enumerated starting with row n = 0 at the top (the 0th row). The entries in each row are numbered from the left beginning with k = 0 and are usually staggered relative to the numbers in the adjacent rows. Having the indices of both rows and columns start at zero makes it possible to state that the binomial coefficient appears in the nth row and kth column of Pascal’s triangle.

Pascal Triangle Example Program

import java.util.Scanner;
public class PascalTriangle {
    public static void main(String[] args) {
		Scanner in=new Scanner(System.in);
		System.out.println("Enter the number of rows");
		int numrows =in.nextInt();
		for(int i =0; i < numrows;i++){
			int num= 1;
			System.out.format("%"+(numrows-i)*2+"s","");
			for(int j=0;j <= i;j++) {
				System.out.format("%4d",num);
				num= num* (i - j) / (j + 1);
			}
			System.out.println(); 
		}
    }
}

Sample Output

enter the number of rows
9
                     1
                   1   1
                 1   2   1
               1   3   3   1
             1   4   6   4   1
           1   5  10  10   5   1
         1   6  15  20  15   6   1
       1   7  21  35  35  21   7   1
     1   8  28  56  70  56  28   8   1

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. import java.util.Scanner; imports a class used later in the program.

3. A Scanner reads typed input from the keyboard (System.in).

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

5. int numrows =in.nextInt(); updates a variable used in the calculation or output.

6. A loop repeats the block until its condition becomes false.

7. int num= 1; updates a variable used in the calculation or output.

8. A loop repeats the block until its condition becomes false.

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.