Java Command Line Arguments: Passing Parameters via String[] args

Command-line arguments allow users to customize program execution by passing input parameters directly from the terminal or console when launching the JVM.

How Command-Line Arguments Work

Every value passed after the class name is captured as an element inside the String[] args array:

# Terminal invocation:
java Calculator 15 25 add

Practical Example: Building a Command-Line Calculator

public class Calculator {
    public static void main(String[] args) {
        // Validate argument length
        if (args.length < 3) {
            System.out.println("Usage: java Calculator <num1> <num2> <add|sub|mul|div>");
            return;
        }

        // Convert String arguments to numerical primitives
        double num1 = Double.parseDouble(args[0]);
        double num2 = Double.parseDouble(args[1]);
        String operation = args[2].toLowerCase();

        double result = switch (operation) {
            case "add" -> num1 + num2;
            case "sub" -> num1 - num2;
            case "mul" -> num1 * num2;
            case "div" -> {
                if (num2 == 0) throw new ArithmeticException("Cannot divide by zero!");
                yield num1 / num2;
            }
            default -> throw new IllegalArgumentException("Unknown operator: " + operation);
        };

        System.out.println("Result: " + result);
    }
}