Mastering Recursion in Java

1. What is Recursion?

Recursion is a programming technique where a method calls itself to solve a smaller instance of the same problem. Think of it like a set of Russian nesting dolls—each doll contains a smaller version of itself inside until you reach the smallest, solid doll.

1. Base Case (Stop Condition)

The condition that terminates the recursion. Without a base case, your program will execute infinitely until it triggers a StackOverflowError.

2. Recursive Work (Step)

The part where the method calls itself with modified parameters that move closer to the base case.

2. Java Implementation: Factorial

Calculating the factorial of a number ($n! = n \times (n-1) \times \dots \times 1$) is the classic example of recursion.

class RecursionDemo {

    // Recursive (non-static) function to calculate factorial
    public int factorial(int n) {
        // 1. Base Case
        if (n <= 1) {
            return 1;
        }
        
        // 2. Recursive Case
        return n * factorial(n - 1);
    }
}

public class Main {

    public static void main(String[] args) {
        RecursionDemo demo = new RecursionDemo();

        int number = 4;
        int result = demo.factorial(number);
        System.out.println("Factorial of " + number + " is: " + result);
    }
}