Factorial Example in Java

Introduction

Factorial is a classic Java console program that demonstrates the concept with complete source code and sample output. Calculation programs apply formulas to solve geometry, statistics and numeric problems.

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

The factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. For example, 5! = 5*4*3*2*1 = 120

Factorial Example Program

import java.util.Scanner;

public class FindFactorial {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		System.out.print("Enter the number: ");
		int num = in.nextInt();
		int result = factorialMethod(num);
		System.out.println("The factorial of " + num + " is " + result);
	}
	public static int factorialMethod(int num) {
		int result = 1;
		for (int i = 1; i <= num; i++) {
			result = result * i;
		}
		return result;
	}
}

Sample Output

Enter the number: 8
The factorial of 8 is 40320

When to use

Use these formulas in homework tools, engineering calculators or anywhere repeated numeric computation is needed.

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 num = in.nextInt(); updates a variable used in the calculation or output.

6. int result = factorialMethod(num); updates a variable used in the calculation or output.

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 Factorial 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.