Exception in Thread-Inventory Program

Can someone please help me understand why I'm getting an exception here?
_____________________________________________________________________________

run:
Welcome to inventory managment.

How many items?
3
Enter item name: Homo
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at inventory.Inventory.main(Inventory.java:39)
Java Result: 1
BUILD SUCCESSFUL (total time: 16 seconds)
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/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package inventory;

import java.util.Scanner;

/**
 *
 * @author Gus
 */
public class Inventory {

/**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

Scanner input = new Scanner (System.in);// run scanner

int count = 0; // array-loop count
        String [] productName = new String [count];
        double [] itemNumber = new double [count];
        double [] numberUnits = new double [count];
        double [] unitPrice = new double [count];
        double [] unitValue = new double [count];
        double totalValue = 0;

System.out.println("Welcome to inventory managment.\n");// welcome

System.out.println("How many items?");
        count = input.nextInt();// count

for (int a = 0; a < count; a++)
        {
            System.out.print("Enter item name: ");
            productName [i] = input.next();

}

}// end main

}// end class

Thanks in advance.

Hi,
I believe you should have got compilation error because what is "i" referred inside the loop?

It was intended to be a variable for the array, initially line 37 used an i for the count variable, that's where I got the error. This code is the result of me trying to tweak it to get it to work. When I switched the count variable to a in line 37 I got an error in the array variable on line 40.

Hi,
I found 2 issues in your program
The first one:

I believe that You are initializing all the above array of zero length. count is zero and hence all the above arrays will have length zero. Now count does not count for array indices any more

You are taking input and storing it in count which overwrites the previous data.
The second one:

either keep "i" or keep "a". If you think a is for counter replace i with a or vice versa whichever suits you.
The ArrayIndexOutOfBoundsException is thrown because in line no 40 you are accessing something that does not actually exist. I mean anything like productName[0] or productname[1] does not exisst since you initialized the array to be of zero length.

Yeah, thanks, I ended up getting it worked out, but those were exactly my problems.

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package inventory;

import java.util.Scanner;

/**
 *
 * @author Gus
 */
public class InventoryC {

/**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

Scanner input = new Scanner (System.in);// run scanner

int count = 0; // array-loop count
        double totalValue = 0;

System.out.println("Welcome to inventory managment.\n");// welcome

System.out.println("How many items?");
        count = input.nextInt();// count

String [] productName = new String [count];
        int a = 0;
        double [] itemNumber = new double [count];
        double [] numberUnits = new double [count];
        double [] unitPrice = new double [count];
        double [] unitValue = new double [count];

for (int i = 0; i < count; i++)
        {
            System.out.print("Enter item name: \n");
            productName[i] = input.next();// get productName
      
        }
        int b = 0;// start variable count for itemNumber
        int count2 = 0;// start count for loop
        while (count2 < count)// start loop for itemNumber
        {

count2++;
          System.out.println("Enter item number for "+ productName[a]);
          itemNumber[b]= input.nextDouble();// get itemNumber
          b++;// bump itemNumber array
          a++;// bump productName array
          
        }
        a = 0;
        int c = 0;
        int count3 = 0;
        while (count3 < count)
        {

count3++;
           System.out.println("Enter number of units for "+ productName[a]);
           numberUnits[c]= input.nextDouble();
           c++;
           a++;

}
        a = 0;
        int d = 0;
        int count4 = 0;
        while (count4 < count)
        {

count4++;
            System.out.println("Enter price per unit for "+ productName[a]);
            unitPrice[d]= input.nextDouble();
            d++;
            a++;

}
        c = 0;
        d = 0;
        int e = 0;
        int count5 = 0;
        while (count5 < count)// loop for calculation of unitValue
        {

count5++;
          unitValue[e] = numberUnits[c] * unitPrice[d];
          c++;
          d++;
          e++;

}
        e = 0;
        int count6 = 0;
        while (count6 < count)
        {

count6++;
         totalValue = totalValue + unitValue[e];
         e++;

}
        a = 0;
        b = 0;
        c = 0;
        d = 0;
        e = 0;
        int count7 = 0;
        while (count7 < count)
        {

count7++;

System.out.println();
System.out.println(productName[a]);
System.out.println("Item number: "+itemNumber[b]);
System.out.println("Units in stock: "+numberUnits[c]);
System.out.println("Value: $"+unitPrice[d]+" each");
System.out.println("This item stock value: $"+unitValue[e]);

a++;
b++;
c++;
d++;
e++;

}

System.out.println();
System.out.println("Total inventory value is: $"+totalValue);

}// end main

}// end class

This is what I ended up with, I know there's a lot of redundant loops in there, but it's due today. Hopefully I'll get time to clean it up later.

Thanks again.