Varargs: Handling Variable Arguments

Sometimes you want to create a method, but you don't know exactly how many inputs the user will provide. For example, a method that adds numbers could take 2 numbers, or it could take 20.

Instead of creating 20 different methods (overloading), Java gives us Varargs (Variable Arguments).

1. The Syntax: The Three Dots (...)

To define a varargs parameter, you follow the data type with an ellipsis (three dots).

public static void printNames(String... names) {
    // Inside the method, 'names' behaves exactly like an array!
}

2. How It Works

When you call a varargs method, Java automatically gathers all the arguments you passed and puts them into an array for you.

public class VarargsDemo {
    public static void main(String[] args) {
        // You can pass as many arguments as you want
        displayFruits("Apple", "Banana");
        displayFruits("Orange", "Mango", "Grape", "Pineapple");
        displayFruits(); // You can even pass zero arguments!
    }

    public static void displayFruits(String... fruits) {
        System.out.println("Printing " + fruits.length + " fruits:");
        for (String f : fruits) {
            System.out.print(f + " ");
        }
        System.out.println("\n---");
    }
}

3. The Rules of Varargs

There are two strict rules you must follow when using varargs in a method:

1. Only One Vararg: A method can only have one variable argument parameter.
2. The "Last Place" Rule: The varargs parameter must be the last parameter in the method signature.

// ✅ VALID
public void setup(int id, String... roles) {}

// ❌ INVALID (Vararg must be last)
public void setup(String... roles, int id) {}

// ❌ INVALID (Only one vararg allowed)
public void setup(int... ids, String... roles) {}

4. Why Use Varargs?

Varargs make your code more flexible and cleaner to call. A great example of a built-in varargs method is System.out.printf(). It takes a string first, and then an unlimited number of variables to fill the placeholders!

💻 Full Practical Example: The Infinite Adder

Copy this code to see how to build a flexible calculator:

public class Calculator {
    public static void main(String[] args) {
        int sum1 = sumAll(5, 10, 15);
        int sum2 = sumAll(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        System.out.println("Sum 1: " + sum1);
        System.out.println("Sum 2: " + sum2);
    }

    public static int sumAll(int... numbers) {
        int total = 0;
        for (int n : numbers) {
            total += n;
        }
        return total;
    }
}

💡 Challenge: The String Joiner

Write a method called joinWords(String... words).

1. The method should take any number of strings.
2. It should return a single String that joins them all together with a space in between.
3. Bonus: If no words are passed, return "No words provided".