Java: Command Line Arguments

how to the access contents of (String [] args)

• Use args.length to determine how many command line arguments there are.
• Unlike in C/C++ and many other languages, the [0] element is not the class name, program name, or anything special. It is really the first argument.
  • So if you run java Main then args.length is really 0
  • If you run java Main foo bar fum then args.length is 3, args[0] is "foo", args[1] is "bar", and args[2] is "fum"

Conversion to numeric values

Command line args come in as Strings.

If you want an int, use Integer.parseInt as in this example from Oracle’s tutorial

int firstArg;
if (args.length > 0) {
    try {
        firstArg = Integer.parseInt(args[0]);
    } catch (NumberFormatException e) {
        System.err.println("Argument" + args[0] + " must be an integer.");
        System.exit(1);
    }
}

There are similar techniques for float, and double.

References

• https://docs.oracle.com/javase/tutorial/essential/environment/cmdLineArgs.html