Variable Arguments (Varargs)

1// Basic varargs method
2public static int sum(int... numbers) {
3    int total = 0;
4    for (int num : numbers) {
5        total += num;
6    }
7    return total;
8}
9
10// Call with varying arguments
11System.out.println(sum());              // 0 (zero args)
12System.out.println(sum(5));             // 5 (one arg)
13System.out.println(sum(1, 2, 3));       // 6 (three args)
14System.out.println(sum(1, 2, 3, 4, 5)); // 15 (five args)
15
16// Can also pass an array
17int[] arr = {10, 20, 30};
18System.out.println(sum(arr));           // 60

1// Varargs with other parameters
2public static void printAll(String label, int... values) {
3    System.out.print(label + ": ");
4    for (int v : values) {
5        System.out.print(v + " ");
6    }
7    System.out.println();
8}
9
10printAll("Numbers", 1, 2, 3);        // Numbers: 1 2 3
11printAll("Empty");                    // Empty:
12printAll("Single", 42);               // Single: 42
13
14// WRONG: Varargs not last
15// public void wrong(int... nums, String s) {}  // Compile error!
16
17// WRONG: Multiple varargs
18// public void wrong(int... a, String... b) {}  // Compile error!

1// Printf uses varargs
2System.out.printf("Name: %s, Age: %d%n", "Alice", 25);
3System.out.printf("Pi: %.2f%n", 3.14159);
4
5// String.format also uses varargs
6String formatted = String.format("Hello, %s!", "World");
7System.out.println(formatted);
8
9// Custom printf-like method
10public static String format(String template, Object... args) {
11    for (int i = 0; i < args.length; i++) {
12        template = template.replace("{" + i + "}", String.valueOf(args[i]));
13    }
14    return template;
15}
16
17String result = format("User {0} is {1} years old", "Bob", 30);
18System.out.println(result);  // User Bob is 30 years old

1// Varargs with generics
2public static <T> List<T> asList(T... elements) {
3    List<T> list = new ArrayList<>();
4    for (T elem : elements) {
5        list.add(elem);
6    }
7    return list;
8}
9
10List<String> names = asList("Alice", "Bob", "Charlie");
11List<Integer> nums = asList(1, 2, 3, 4, 5);
12
13// Method overloading vs varargs
14// Overloading is faster for known argument counts
15public static int max(int a, int b) {
16    return a > b ? a : b;
17}
18
19public static int max(int a, int b, int c) {
20    return max(max(a, b), c);
21}
22
23public static int max(int... numbers) {
24    if (numbers.length == 0) throw new IllegalArgumentException();
25    int max = numbers[0];
26    for (int n : numbers) {
27        if (n > max) max = n;
28    }
29    return max;
30}