A Closer Look at Methods and Classes - Using Command-Line Arguments

(Page 12 of 12 )

Sometimes you will want to pass information into a program when you run it. This is accomplished by passing command-line arguments to main( ). A command-line argument is the information that directly follows the program’s name on the command line when it is executed. To access the command-line arguments inside a Java program is quite easy—they are stored as strings in the String array passed to main( ). For example, the following program displays all of the command-line arguments that it is called with:

// Display all command-line arguments.
class CommandLine {
  public static void main(String args[]) {
    for(int i=0; i<args.length; i++)
      System.out.println("args[" + i + "]: " +
                          args[i]);
  }
}

Try executing this program, as shown here:

java CommandLine this is a test 100 -1

When you do, you will see the following output:

args[0]: this
args[1]: is
args[2]: a
args[3]: test
args[4]: 100
args[5]: -1

Remember  All command-line arguments are passed as strings.
                 You must convert numeric values to their internal
                 forms manually, as explained in Chapter 14.

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This article is excerpted from chapter 7 of Java: the Complete Reference, J2SE 5 Edition, written by Herbert Schildt (McGraw-Hill/Osborne, 2004; ISBN: 0072230738). Check it out at your favorite bookstore. Buy this book now.