Free Computer Courses

How to use command-line arguments

Updated September 2026 · Beginner-friendly guide

Inspect args

The JVM places command-line arguments in the String[] args parameter of main.

public static void main(String[] args) {
    System.out.println("Arguments: " + args.length);
}

Read an argument safely

Check the array length before accessing an index.

if (args.length > 0) {
    System.out.println("Hello, " + args[0]);
} else {
    System.out.println("Usage: java Greeter NAME");
}

Parse a numeric argument

Every argument begins as text, so numeric input must be parsed and invalid formats handled.

try {
    int count = Integer.parseInt(args[0]);
    System.out.println(count * 2);
} catch (NumberFormatException error) {
    System.out.println("COUNT must be a whole number.");
}

Run with arguments

Place arguments after the class name. Quotes keep words with spaces together as one argument.

java Greeter Ada
java Greeter "Ada Lovelace"

Related tutorials