Question

I’m trying to do some processing on whether the user enters a (1) file name, or (2) directory name into the command line. Anything else should throw an error. Starting with the simplest case, I wrote this:

import java.io.*;
import java.util.*;

public class RemoveDuplicates {

    public static void main(String[] args) {
        if (args.length != 1) {
            System.out.println("Program accepts one command-line argument.  Exiting!");
            System.exit(1);
        }
        File f = new File(args[0]);
        if (f.isDirectory()) {
            System.out.println("is directory");
        }
        else if (f.isFile()) {
            System.out.println("is file");
        }
        else {
            System.out.println("Shouldn't happen");
        }
    }
}

at the command line, I type: java RemoveDuplicates example.txt
and I get the reuslts, “Shouldn’t happen.” I also tried java RemoveDuplicates “example.txt” and that doesn’t work either. So I was wondering if my code is wrong, or how I’m passing it into the command line is wrong for starters.

Secondly, how do you pass in a directory name? Like if your directory was myDirectory, is it the same thing: java RemoveDuplicates myDirectory

Third, why if I put my File f = new File(args[0]) into a try block and have a catch block, I get a compile error about what is in my try block never throws an exception. I thought File threw an exception? Thanks in advance!

Answer 1

1. Are you sure example.txt exists in your working directory? Try adding the following and see what happens.

   File f = new File(args[0]);
   if (!f.exists()) {
     System.out.println("does not exist");
   }
   

2. You have that right.

3. Actually, I don’t get this error. How did you do the try/catch?