CODEWITHSUNDEEP
javaarraylistindexoutofboundsexception
Marcos
Marcos

Reputation: 53

OutOfBoundsException Troubles, Java

I'm getting the following error:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 86, Size: 86
at java.util.ArrayList.rangeCheck(ArrayList.java:604)
at java.util.ArrayList.get(ArrayList.java:382)
at Netbooks.Recommendations.getDotProduct(Recommendations.java:72)
at Netbooks.TestRecomendations.main(TestRecomendations.java:11)
Java Result: 1

I've looked the code over many times and I can't seem to find where I going over the index of the arraylist...

Here is the code for the dotProduct ArrayList:

public List<Integer> getDotProduct() throws IOException {
    Books book = new Books();
    Ratings cust = new Ratings();
    PureRatings pureRatings = new PureRatings();


    List<String> bookList = book.readBooks();
    List<String> customerList = cust.readCustomers();
    List<List<Integer>> pureRatingsList = pureRatings.parseRatingsFile();
    List<Integer> dotProduct = new ArrayList<Integer>();
    int index = getCustIndex();

    if (index == -1) {
        return dotProduct;
    }

    for (int i = 0; i < customerList.size(); i++) {
        int sum = 0;

        for (int j = 0; j < bookList.size(); i++) {
            if (i == index) {
                dotProduct.add(0);
            } else { //Next line is line 72.
                sum = sum + (pureRatingsList.get(index).get(j)) * (pureRatingsList.get(i).get(j)); //Line 72.
            }
        }
        dotProduct.add(sum);
    }

    return dotProduct;
}

And my main method (in another class) just in case:

public class TestRecomendations {

    public static void main(String[] args) throws IOException {
        Recommendations recomm = new Recommendations();

        List<Integer> dotProduct = recomm.getDotProduct();//Line 11.

        for (int i = 0; i < dotProduct.size(); i++) {
            System.out.println(dotProduct.get(i));
        }
    }
}

It should just print out the elements of the dotProduct ArrayList...

I don't understand how line 72 is causing a problem since I should be able to add an unlimited number of items to the ArrayList....Any help would be appreciated.

Upvotes: 1

Views: 2401

Answers (4)

gefei
gefei

Reputation: 19766

isn't this line the problem?

for (int j = 0; j < bookList.size(); i++) {

I guess what you need is

for (int j = 0; j < bookList.size(); j++) {

Upvotes: 2

razlebe
razlebe

Reputation: 7144

The issue in line 72 is with a get(), not with an add().

I suspect this could be the root cause of the problem:

for (int i = 0; i < customerList.size(); i++) {
    int sum = 0;

    for (int j = 0; j < bookList.size(); i++) {  
        if (i == index) {
            dotProduct.add(0);
        } else { //Next line is line 72.
            sum = sum + (pureRatingsList.get(index).get(j)) * (pureRatingsList.get(i).get(j)); //Line 72.
        }
    }
    dotProduct.add(sum);
}

In the second for loop, you're incrementing i and not j. That will probably result in you using a value for i in the line 

sum = sum + (pureRatingsList.get(index).get(j)) 
     * (pureRatingsList.get(i).get(j));

larger than the size of pureRatingsList, resulting in the exception you're seeing.

Upvotes: 6

Brian Roach
Brian Roach

Reputation: 76898

It's causing a problem because you're requesting an index that doesn't exist; ergo "Out of bounds".

You're requesting index 86 when the size is only 86 (which is index 0 - 85). Arrays are zero based.

Learning to use the debugger will really help you solve problems like this as you can step through your program and see exactly what's happening.

Upvotes: 0

Kurt Du Bois
Kurt Du Bois

Reputation: 7655

You do know that there are things like iterators and foreach to make traversing a collection simpler?

The problem is that the index of a list starts at 0 and you try to start at 1.

Upvotes: 1

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