Why did I get an “ArrayIndexOutOfBoundsException”?

Question

I'm pretty new to programming and working on an assignment for class. Now, I'm not asking for anyone to write my code for me but I'm stuck with a runtime error. In the assignment we need to read a file, use the first line, "15", to initialize the size of an array, and proceed to fill the array with the information from each line.

edit: I didn't want to post all of the code because I thought it would look too long but because of the downvotes for being vague, here it goes.

File:

15
produce,3554,broccoli,5.99,1
produce,3554,broccoli,5.99,1
produce,3555,carrots,2.23,0.25
produce,3555,carrots,2.23,0.25
produce,3555,carrots,2.23,0.25
cleaning,2345,windex,5.99,1 unit
cleaning,2345,windex,5.99,1 unit
cleaning,2345,windex,5.99,1 unit
cleaning,2345,windex,5.99,1 unit
cleaning,2346,toilet paper,12.99,4 rolls
cleaning,2346,toilet paper,12.99,4 rolls
cleaning,2335,windex,2.25,1 mini sprayer
cleaning,1342,wipes,3.99,10 units
cleaning,1342,wipes,3.99,10 units
produce,3546,lettuce,2.99,0.5

My Error:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 15
    at Inventory.readFile(Inventory.java:45)
    at Inventory.<init>(Inventory.java:12)
    at Supermarket.main(Supermarket.java:3)

Class with the Line 45 in Question (line 45 is commented, scroll to the right)"

import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

public class Inventory{
    Product[] list;
    String[] invData;
    private int i = 0;
    public int count;

    public Inventory (String f){
        readFile(f);
    }

    public int indexOfProduct(int code){        
        for(i=0; i<list.length; i++){ 
            if (list[i] != null)
                if (list[i].getCode() == code)
                    return i;

        }
        return -1;
    }


    public Product delete(int pos){
        Product temp = new Product();
        temp = list[pos];
        list[pos] = null;
        return temp;
    }

    public void readFile(String fileName){
        try{
            File invList = new File (fileName);
            Scanner s = new Scanner(invList);
            int itemCount = s.nextInt();
            list = new Product[itemCount];
            count = itemCount;
            while (s.hasNext()){
                String line = s.nextLine();
                invData = line.split(",");
                if (invData[0].equals("produce")){
                    list[i] = new Produce(invData[1], invData[2], invData[3], invData[4]); // This is Line 45, Where the error occurs
                } else if(invData[0].equals("cleaning")){
                    list[i] = new Cleaning(invData[1], invData[2], invData[3], invData[4]);
                }
                i++;
            }//end of while loop
        } catch (FileNotFoundException Abra) {
            String error = Abra.getMessage();
            System.out.println(error);
            } 
    } // end of method

    public Product findCode(int c){
        for(int i=0; i<list.length;i++)
            if(list[1].getCode() == c)
                return list[i];
        return null;
    }//end of method
}//end of class

Why did I get an "ArrayIndexOutOfBoundsException"? I hope someone can point out the flaw in my logic so I don't repeat it again.

Answer 1

Your issue is clearly with the use of i , as that is the only variable index on that line, and the out of range index is "15", which is just past the end of your 15-item array. So, couple of issues, all surrounding the use of i :

As nhellwig mentioned, be sure that i is actually initialized to 0 before calling this function.

Additionally, you're putting a lot of faith in the consistency of the item number in the file and the actual number of items. You should either produce a warning and stop trying to store items in the array if i >= itemCount , or use a container like an ArrayList that can grow to accommodate new items instead of a fixed size array.

Edit: Also, I should point out that you increment i whether you read an item or not, which means even blank lines will increment i , causing gaps in your list or array overruns. Since itemCount is the number if items, you should stick to that and only increment i if you read an actual item.

In that same spirit, you should verify that invData.length == 5 after you call split(), because a misplaced comma, etc. in your file may also end up with an OOB error. Granted, for your project, it's probably OK to make assumptions about the number of elements in a line that starts with "produce" or "cleaning", but in general it's important to be cautious with data coming from a user-created file.

Answer 2

I found the answer to be that I needed an "s.nextLine();"

Because I used "s.nextInt();" the pointer was just hangin around at the end of "15" in my file. Then, when the first line in the While loop "String line = s.nextLine();" executed the pointer moved from the end of 15 to before the p in produce in the 2nd line of the list file.

The working method looks like this:

public void readFile(String fileName){
    try{
        File invList = new File (fileName);
        Scanner s = new Scanner(invList);
        int itemCount = s.nextInt();
        s.nextLine(); // This is the new line that made it work
        list = new Product[itemCount];
        count = itemCount;
        while (s.hasNext()){
            String line = s.nextLine(); //moves file pointer over one
            invData = line.split(",");
            if (invData[0].equals("produce")){
                list[i] = new Produce(invData[1], invData[2], invData[3], invData[4]);
            } else if(invData[0].equals("cleaning")){
                list[i] = new Cleaning(invData[1], invData[2], invData[3], invData[4]);
            }
            i++;
        }//end of while loop
    } catch (FileNotFoundException Abra) {
        String error = Abra.getMessage();
        System.out.println(error);
        } 
} // end of method

Answer 3

How many times do you call readFile? You should have i = 0; at the beginning of the function.

Answer 4

“i”不应该是全局值，而应该是方法局部变量，初始化为零。