Recursion is a method calling itself until a base case is met.

Key Terms

• Recursion: A method calling itself to solve a problem.
• Recursive Method: A method containing a call to itself.
• Base Case: Condition that stops recursive calls.
• Recursive Case: Where the method calls itself with modified input.

How Recursion Works

1. Check base case stopping condition.
2. Perform a task.
3. Call itself with smaller input.
4. Continue until base case is reached.

Example 1: Sum of Numbers

package Recursion;

public class recursion {
    public static void main(String[] args) {
        int result = sum(10);
        System.out.println(result);
    }

    public static int sum(int k) {
        if (k > 0) {
            return k + sum(k - 1);
        } else {
            return 0;
        }
    }
}

Output

55

Example 2: Factorial Using Recursion

package Recursion;

public class R_Fact {
    public static void main(String[] args) {
        int num = 6;
        long factorial = multiplyNumbers(num);
        System.out.println("Factorial of " + num + " = " + factorial);
    }

    public static long multiplyNumbers(int num) {
        if (num >= 1)
            return num * multiplyNumbers(num - 1);
        else
            return 1;
    }
}

Output

Factorial of 6 = 720

Advantages

• Shorter, cleaner code for repetitive patterns.
• Breaks complex problems into smaller tasks.
• Ideal for trees, graphs and hierarchical data.

Disadvantages

• Each call consumes call stack memory.
• Slower than iterative solutions.
• Missing base case causes stack overflow.

FAQ

1. What is recursion in Java?

A method calling itself until a base condition stops it.

2. What is the base case for?

Stops recursive calls. Prevents infinite recursion.

3. When should recursion be used?

Factorial, tree traversal, divide-and-conquer algorithms.