Writing and reading to/from a 2D array!

[celebor]

Greetings! Basically, I'm having troubles writing integer data into a 2D array. I'm also not sure if I'm writing it correctly to, though it seems right.

Now to the examples:

This is how I write to 1D array:

public static void write ()
    {
        try
        {
            DataOutput d = new DataOutputStream (new FileOutputStream ("save.txt"));
            DataOutput f = new DataOutputStream (new FileOutputStream ("alreadySaved.txt"));

            for (int i = 0 ; i < 55 ; i++)
            {
                d.writeInt (userBooksRated [i]);

                f.writeBoolean (true);
        }
        catch (Exception e)
        {
            String msg = e.toString ();
            System.out.println (msg);
        }
        c.print ("Saved");
        System.exit (-0);
    }

That's no problem...

Next, I write a 2D array, declared in the beginning of the program, to a file. I do that so I can create a database file to use in the future.

Here's how I do it:

    public static void write ()
    {
        try
        {
            DataOutput g = new DataOutputStream (new FileOutputStream ("database.dat"));

            for (int i = 0 ; i < storeRatings.length ; i++)
            {
                for (int j = 0 ; j < storeRatings [i].length ; j++)
                {
                    g.writeInt (storeRatings [i] [j]);
                }
            }

        }
        catch (Exception e)
        {
            String msg = e.toString ();
            System.out.println (msg);
        }
        c.print ("Saved");
        System.exit (-0);
    }

and finally, on the next program launch, I want to write the integers from the database file into the array. This is what I do:

public static void readDatabase ()
    {
        try
        {
            DataInput b = new DataInputStream (new FileInputStream ("database.dat"));
            for (int i = 0 ; i < storeRatings.length ; i++)
            {
                for (int j = 0 ; j < storeRatings [i].length ; j++)
                {
                    storeRatings [i] [j] = b.readInt ();
                }
            }
        }



        catch (Exception e)
        {
            String msg = e.toString ();
            System.out.println (msg);
        }
    }

Finally, when one part of the program tries to use the array I get an error. :(
java.lang.ArrayIndexOutOfBoundsException: 55
at BookISP.calculate(BookISP.java:238)
at BookISP.getRatings(BookISP.java:230)
at BookISP.menu(BookISP.java:423)
at BookISP.main(BookISP.java:64)

and here's the part of the code that uses the 2D array:

    public static void calculate ()
    {
        for (int i = 0 ; i < 86 ; i++)
        {
            matchBooks [i] = userBooksRated [0] * storeRatings [i] [0];
            for (int j = 1 ; j < 55 ; j++)
            {
                matchBooks [i] += userBooksRated [j] * storeRatings [i] [j];

            }
        }
        c.close ();
        c = new Console ();
        findSimilar ();

    }

My question is - what am I doing wrong? Am I writing it to the file wrong? Am I reading it from the file wrong?

Thanks for reading!

[tyroceur]

What are the dimensions of your arrays....?? write all of them

[m00nchile]

This is pretty suspicious:

public static void calculate ()
    {
        for (int i = 0 ; i < 86 ; i++)
        {
            matchBooks [i] = userBooksRated [0] * storeRatings [i] [0];
            for (int j = 1 ; j < 55 ; j++)
            {
                matchBooks [i] += userBooksRated [j] * storeRatings [i] [j];

            }
        }
        c.close ();
        c = new Console ();
        findSimilar ();

    }

Why the hardcoded limits for i and j? I'd suggest limiting i and j with the .length field of your arrays, like you did in your previous methods.

[celebor]

suspicious? lol...

You see, this 2d array that I'm trying to write and read - it was hardcoded before. And it's pretty damn huge. That's why I want to read and write it from a file. The calculations worked fine before, so I doubt the problem lies in there.

[tyroceur]

your exception tells that the problem lies in the index used to access the array element.... so write the array dimensions here or please double-check the dimensions of the arrays you have created.

[celebor]

Here is how I declared it:
public static int storeRatings[] [] = new int [55] [86];
Then:

        public static void readDatabase ()
    {
        try
        {
            DataInput b = new DataInputStream (new FileInputStream ("database.dat"));
            for (int i = 0 ; i < storeRatings.length ; i++)
            {
                for (int j = 0 ; j < storeRatings [i].length ; j++)
                {
                    storeRatings [i] [j] = b.readInt ();
                }
            }
        }

Then:

    public static void main (String[] args)
    {
        c = new Console ();
        books.getBooks ();
        books.printBooks ();
        readDatabase (); //Calling for it here, before the calculations
        read ();
        if (alreadySaved == false)
        {
            for (int i = 0 ; i < 55 ; i++)
            {
                alreadyRated [i] = false;
                alreadyPrinted [i] = false;
                userBooksRated [i] = 0;
                getRatings ();
            }
        }
        else
            menu ();

    }

Edit:

Just so you know, there are 86 users and each provide 55 ratings. 1 rating per book and 0 means they haven't rated it.

Oh and also, I changed the method I used to write the array into the file. [it's a one time run piece of code]

            for (int i = 0 ; i < storeRatings.length ; i++)
            {
                for (int j = 0 ; j < storeRatings [i].length ; j++)
                {
                    g.writeInt (storeRatings [i] [j]);
                }
            }

[tyroceur]

Here is how I declared it:
public static int storeRatings[] [] = new int [55] [86];

Here is your problem..... you declared it [55] [86] and below accessing it as [86] [55]

and here's the part of the code that uses the 2D array:
Code:

public static void calculate ()
{
for (int i = 0 ; i < 86 ; i++)
{
matchBooks [i] = userBooksRated [0] * storeRatings [i] [0];
for (int j = 1 ; j < 55 ; j++)
{
matchBooks [i] += userBooksRated [j] * storeRatings [i] [j];

}
}
c.close ();
c = new Console ();
findSimilar ();

}

My question is - what am I doing wrong? Am I writing it to the file wrong? Am I reading it from the file wrong?

Just correct this and I hope it will be solved. I would recommend using size() and length fields instead of hardcoded limits.

Hope that helps.

[celebor]

OMG!! Lmao, dumb me, dumb me! Thank you so much for pointing that out!! It seems to be working now!!

[tyroceur]

celebor,
Is this thread solved?

[m00nchile]

This is exactely why I said that the hardcoded part was suspicious. Always use the arrays .length field for loops iterating through an array, this way you avoid errors in logic like this.

[celebor]

@tyroceur
Yep, it's solved!

@m00nchile
Hehe, yah :]

[tyroceur]

So please mark it solved by selecting 'Mark Thread as Solved' from 'Thread Tools' on top of the thread.

Thanks :)