Question

This program sorts the first n words from a file using insertion sort.

This is not made by me. We were asked to use this program our teacher provided to implement other sorting techniques. I imported the source code and when I run it. It says:

Exception in thread “main” java.lang.ArrayIndexOutOfBoundsException: 0
at SortingAnalysis.main(SortingAnalysis.java:26)

But when our teacher demonstrated it in our class, there is no error in it.

I’m also wondering how it sorts the words from a file without even stating the file name (e.g. tobesorted.txt). Maybe as long as it’s within the JRE System Library, it will work, won’t it?

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

/**
 * Compares the running times of sorting algorithms
 * @author bryann
 *
 */
public class SortingAnalysis {

    public static void insertionSort(String[] a) {
        int n = a.length;
        for(int i = 1; i < n; i++) {
            String cur = a[i];
            int j = i - 1;
            while((j >= 0) && (a[j].compareTo(cur) > 0)) {
                a[j + 1] = a[j--];
            } // end while
            a[j + 1] = cur;
        } // end for
    } // end insertionSort

    public static void main(String[] args) {
        final int NO_OF_WORDS = 5000;
        try {
            Scanner file = new Scanner(new File(args[0]));
            String[] words = new String[NO_OF_WORDS];

            int i = 0;
            while(file.hasNext() && i < NO_OF_WORDS) {
                words[i] = file.next();
                i++;
            } // end while
            long start = System.currentTimeMillis();
            insertionSort(words);
            long end = System.currentTimeMillis();
            System.out.println("Sorted Words: ");
            for(int j = 0; j < words.length; j++) {
                System.out.println(words[j]);
            } // end for        
            System.out.print("Running time of insertion sort: " + (end - start) + "ms");

        } // end try
        catch(SecurityException securityException) {
            System.err.println("You do not have proper privilege to access the files.");
            System.exit(1);
        } // end catch
        catch(FileNotFoundException fileNotFoundException) {
            System.err.println("Error accessing file");
            System.exit(1);
        } // end catch
    } // end main
} // end class SortingAnalysis

Is the error because of import? Using Eclipse, I just clicked
File > Import > General > File System > From directory (the whole folder he sent to us) > Into folder (I created a new project and there is where I “imported” the code) > Finish

Please help me. I can’t start with the assignment (that is, trying other sorting techniques in the same source file) because I can’t run it. Thank you very much!

Answer 1

The main function of a program takes arguments :

public static void main(String[] args) {

Those arguments are the ones passed to the program on the command line :

java SortingAnalysis /home/somebody/tobesorted.txt

In this case, args[0] would be "/home/somebody/tobesorted.txt"

This enables the program to know what file to open :

Scanner file = new Scanner(new File(args[0]));

But when you launch your program without providing the path to a file, args is too short and you have this java.lang.ArrayIndexOutOfBoundsException: 0 as args[0] doesn't exist you got.

So give the path to the file to sort to remove this error. For example :

java SortingAnalysis C:\somepath\tobesorted.txt

EDIT:

If you want to hardcode the path, you may do this :

Scanner file = new Scanner(new File("C:\\somepath\\tobesorted.txt"));

(note the double \\).