JAVA - Array Out of Bounds Error

Question

I have an issue with my logic and I would appreciate some pointers. My code produces the Array Out Of Bounds Exception when I try to iterate through an array of files in a directory and store the files that end in .txt within another array.

I think my issue is that the array of all files is larger than the array of txt files, that seems the most logical reason for the error. The problem is I don't know why its finding more occurrences of txt files in the second loop vs the first.

Here is the code:

public static void ListFiles(String file_dir) {
        String files;
        int txtCounter = 0;

        File folder = new File(file_dir);
        File[] listOfFiles = folder.listFiles(); 

        //Count all txt files
        for (int y = 0; y < listOfFiles.length; y++) {
            if (listOfFiles[y].isFile()) {
                files = listOfFiles[y].getName();
                if (files.endsWith(".txt") || files.endsWith(".TXT")) {
                    txtCounter++;//Add to the count
                }
            }
        }

        //Create array for the list of txt files.
        String txtFiles[] = new String[txtCounter];

        for (int i = 0; i < listOfFiles.length; i++) {
            if (listOfFiles[i].isFile()) {
                files = listOfFiles[i].getName();
                if (files.endsWith(".txt") || files.endsWith(".TXT")) {
                    //Add all txt files to new array txtFiles
                    txtFiles[i] = folder + files;                   
                    System.out.println(txtFiles[i]);
                }
            }
        }

        //Send array back to Main
        //return txtFiles[];
    }

Am I making this harder than it has to be? I'm trying to take a list of text files, replace certain words in the files, and combine them all into one file when complete.

Thanks!

UPDATED:

public static String[] ListManualSections(String file_dir) {
    file_dir = file_dir + "\\manualSections\\";

    String files;

    //Create list of all files in the manualSections directory.
    File folder = new File(file_dir);
    File[] listOfFiles = folder.listFiles(); 

    //Dynamic list of text files
    ArrayList al = new ArrayList();

    //Add each occurrence of a text file to the ArrayList
    for (int i = 0; i < listOfFiles.length; i++) {
        files = listOfFiles[i].getName();
        if (listOfFiles[i].isFile() && files.toLowerCase().endsWith(".txt")) {
            al.add(folder + "\\" + files);
            //System.out.println(al);
        }
    }

    //Send list back to Main
    String[] txtFiles = (String[]) al.toArray(new String[al.size()]);
    return txtFiles;
}

Answer 1

Your second for loop iterates over all of the files, meaning that i = 0 .. N where N is the number of total files. But your text files could occur at any i here. The so even if there are only 2 text files, if they are found on the 6th iteration of the N total files, that is not the index you want to be using for your text file array.

I would suggest you create a counter for the index of the text file array and increment it as you add, or use a List.

String txtFiles[] = new String[txtCounter];
int txtIndex = 0;

for (int i = 0; i < listOfFiles.length; i++) {
    if (listOfFiles[i].isFile()) {
        files = listOfFiles[i].getName();
        if (files.endsWith(".txt") || files.endsWith(".TXT")) {
            //Add all txt files to new array txtFiles
            txtFiles[txtIndex] = folder + files;
            txtIndex++;                   
            System.out.println(txtFiles[i]);
        }
    }
}

Answer 2

You could simply use File.listFiles(FileNameFilter) to get the files matching your criteria.

private File[] getTextFiles(String dir)
{
    File folder = new File(dir);

    return folder.listFiles(new FilenameFilter() {
        @Override
        public boolean accept(File dir, String name) {
            return name.toLowerCase().endsWith(".txt");
        }           
    });
}

Answer 3

Well look at this scenario -

listOfFiles is size 6, first loop you find 5 txt files, and the last element in listOfFiles is a txt file.

Then at the last iteration of second loop, you are trying to do txtFiles[5] = folder+files. That will throw the error because txtFiles is only 0-4.

Like Louis said, use ArrayList.

Answer 4

As addition to the answer of @Louis, you could go with a separate counter for the file and txt-file. Like this:

int txtidx = 0;
for (int i = 0; i < listOfFiles.length; i++) {
    if (listOfFiles[i].isFile()) {
        files = listOfFiles[i].getName();
        if (files.endsWith(".txt") || files.endsWith(".TXT")) {
            //Add all txt files to new array txtFiles
            txtFiles[txtidx] = folder + files;                   
            System.out.println(txtFiles[txtidx]);
            txtidx++;
        }
    }
}

Answer 5

instead of complicating matters, you can do this

Use Apache Commons io to list all your files

    Collection<File> files = FileUtils.listFiles(new File("file_dir"), new String[]{"txt"}, true);

//use true if you want it to be recursive, i.e. to search subdirectories of file_dir

for (File file : files)
{
    //you can then play with your file object here
}

Let me know if you have issues.

Answer 6

You're making this harder than it has to be.

You're passing over an array once to count how many text files there are and then, a second time, to add text files to another array.

Any implementer of the List<E> interface would be more appropriate than an array; you can then add elements on the fly. If you must have an array afterwards. you can always use the toArray method at the end.

Answer 7

This second for loop seems confused about whether it's iterating over txtFiles or over listOfFiles, which could have different lengths. In particular, you should probably not be writing to txtFiles[i] when i could be larger than the length of txtFiles.

Mostly, though, this code would be simpler if you just used an ArrayList.