Writing and reading to/from a 2D array!

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:

Code:

---

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:

Code:

---

    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:

Code:

---

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:

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?

Thanks for reading!

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

This is pretty suspicious:

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 ();

    }

---

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.

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.

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.

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

Code:

---

        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:

Code:

---

    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]

Code:

---


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

---

Quote:

---

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]

Quote:

---

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.

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

celebor,
Is this thread solved?

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.

@tyroceur
Yep, it's solved!

@m00nchile
Hehe, yah :]

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

Thanks :)