The Nuts and Bolts of the Java Language |
As you learned in The main Method in The "Hello World" Application, the runtime system executes a Java program by calling the application'smain
method. Themain
method then calls all the other methods required to run your application.The
main
method in the character-counting example initializes thecount
variable, then stops atSystem.in.read
and waits for the user to type characters. When the user finishes typing, the program displays the number of characters typed.Accepting a Filename on the Command Line
Let's modify the program to accept a command line argument and have it count the characters in the file specified on the command line. Compare this version of the character-counting program with the original version listed above.In this implementation of the character-counting program, if the user specifies a name on the command line, then the application counts the characters in the file. Otherwise, the application acts as it did before and reads from the standard input stream. Now, run the new version of the program on this text file and specify the name of the file (import java.io.*; class CountFile { public static void main(String[] args) throws java.io.IOException, java.io.FileNotFoundException { int count = 0; InputStream is; String filename; if (args.length >= 1) { is = new FileInputStream(args[0]); filename = args[0]; } else { is = System.in; filename = "Input"; } while (is.read() != -1) count++; System.out.println(filename + " has " + count + " chars."); } }testing
) on the command line.For information about command line arguments refer to the Setting Program Attributes lesson.
The Nuts and Bolts of the Java Language |