Command line arguments and Variable length arguments

 

✅ 1. Command-Line Arguments in Java

Command-line arguments allow you to pass information to a Java program when it starts from the terminal or command prompt.

🔹 Syntax:

public static void main(String[] args)

• args is an array of String that holds the arguments.

• Arguments are space-separated words passed when running the program.

---

🔸 Example: Program to Print Command-Line Arguments

public class CommandLineExample {
    public static void main(String[] args) {
        System.out.println("You passed " + args.length + " arguments.");

        for (int i = 0; i < args.length; i++) {
            System.out.println("Argument " + i + ": " + args[i]);
        }
    }
}

✅ How to Run:

javac CommandLineExample.java
java CommandLineExample Hello World 123

Output:

You passed 3 arguments.
Argument 0: Hello
Argument 1: World
Argument 2: 123

---

✅ 2. Variable-Length Arguments (Varargs) in Java

Java allows you to define methods that accept variable numbers of arguments using ....

🔹 Syntax:

methodName(datatype... varname)

• Treated as an array inside the method.

• Only one vararg is allowed per method, and it must be last in the parameter list.

---

🔸 Example: Method to Add Numbers

public class VarargsExample {
    static int add(int... numbers) {
        int sum = 0;
        for (int num : numbers) {
            sum += num;
        }
        return sum;
    }

    public static void main(String[] args) {
        System.out.println(add(10, 20));           // 30
        System.out.println(add(5, 15, 25, 35));    // 80
        System.out.println(add());                // 0
    }
}

---

✅ Differences Between Command-Line Arguments and Varargs

Feature	Command-Line Arguments	Varargs
Where used	In main(String[] args)	In any user-defined method
Source of data	From user via terminal/command	From method call inside program
Type	Always String[]	Any type (e.g., int..., String...)
Example Input	java Program 1 2 3	method(1, 2, 3)