Intermediate Java Day 4: Methods & Recursion

Goal of this Day

Today you will learn:

• Method overloading
• Recursion basics
• Recursive algorithms (factorial, Fibonacci)
• Tail recursion and stack limits

By the end, you will be able to write recursive methods and understand how recursion works in Java.

Step 1: Method Overloading

Method overloading allows you to have multiple methods with the same name but different parameters.

public static int add(int a, int b) {
    return a + b;
}

public static double add(double a, double b) {
    return a + b;
}

Explanation:

• Java chooses the correct method based on the arguments
• Helps keep method names consistent

Step 2: Recursion Basics

A recursive method calls itself until a base condition is met.

public static int factorial(int n) {
    if(n == 0) return 1;
    return n * factorial(n - 1);
}

System.out.println(factorial(5)); // 120

Explanation:

• Base case: stops the recursion (n == 0)
• Recursive case: calls itself with a smaller value

Step 3: Recursive Algorithms

Factorial

public static int factorial(int n) {
    if(n == 0) return 1;
    return n * factorial(n - 1);
}

Fibonacci

public static int fibonacci(int n) {
    if(n == 0) return 0;
    if(n == 1) return 1;
    return fibonacci(n - 1) + fibonacci(n - 2);
}

Step 4: Tail Recursion & Stack Limits

Tail recursion is a type of recursion where the recursive call is the last operation.

Example (factorial tail recursion):

public static int factorialTail(int n, int result) {
    if(n == 0) return result;
    return factorialTail(n - 1, n * result);
}

Note:

• Java does not optimize tail recursion automatically
• Too deep recursion may cause StackOverflowError

Practice

public static int factorial(int n) {
    if(n == 0) return 1;
    return n * factorial(n - 1);
}

System.out.println(factorial(5)); // 120

Exercise

Write a recursive method to calculate the nth Fibonacci number.

Steps:

• Create a method fibonacci(int n)
• Base cases: n = 0 → 0, n = 1 → 1
• Recursive case: fibonacci(n - 1) + fibonacci(n - 2)
• Test your method with different values of n

Example:

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

    public static void main(String[] args) {
        System.out.println(fibonacci(10)); // 55
    }
}