Recursive Functions in Java

 

✅ Recursive Functions in Java

A recursive function is a method that calls itself to solve a problem.

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🔹 Key Concepts

1. Base Case – condition to stop recursion

2. Recursive Case – where the method calls itself

🔁 Recursion breaks the problem into smaller subproblems until the base case is reached.

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🔸 Example 1: Factorial of a Number

Problem: Calculate n! = n × (n-1) × (n-2) × ... × 1

public class Factorial {
    static int factorial(int n) {
        if (n == 0)  // Base case
            return 1;
        else
            return n * factorial(n - 1);  // Recursive call
    }

    public static void main(String[] args) {
        int result = factorial(5);
        System.out.println("Factorial of 5 is " + result);
    }
}

Output:

Factorial of 5 is 120

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🔸 Example 2: Fibonacci Series

Problem: Print nth Fibonacci number
Fibonacci Series: 0, 1, 1, 2, 3, 5, 8, ...

public class Fibonacci {
    static int fibonacci(int n) {
        if (n == 0) return 0;   // Base case
        if (n == 1) return 1;   // Base case
        return fibonacci(n - 1) + fibonacci(n - 2);  // Recursive case
    }

    public static void main(String[] args) {
        int n = 7;
        System.out.println("Fibonacci(" + n + ") = " + fibonacci(n));
    }
}

Output:

Fibonacci(7) = 13

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🔸 Example 3: Sum of Digits

Problem: Find the sum of digits of a number using recursion

public class SumDigits {
    static int sumOfDigits(int n) {
        if (n == 0)
            return 0;
        return n % 10 + sumOfDigits(n / 10);
    }

    public static void main(String[] args) {
        int num = 1234;
        System.out.println("Sum of digits = " + sumOfDigits(num));
    }
}

Output:

Sum of digits = 10

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🔹 When to Use Recursion?

Use recursion when:

• The problem is naturally recursive (e.g., factorial, tree traversal)

• The solution involves repeated subproblems

• A loop would make the solution more complex

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⚠️ Caution:

• Recursive functions may cause StackOverflowError if the base case is missing or recursion is too deep.

• Use iteration for efficiency when possible.