Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException

[paul]

Hi, I have enrolled into Java classes and got this problem that i have mostly figured out how to do, but my application gives me an error when i run it. I understand that there is a mistake, but i can't figure out what is causing it and if it can be fixed.

The application is from a Java texbook, and its purpose is to calculate sales comissions.

Code:

at $200 base + 9% of sales = salary.

I'm using an array to feed the sales figures, then trying to do the math upon the values of the array and count how many salesmen fit into the ranges of salaries between:

Code:

200-299
300-399
....
1000 and more.

Here is my code:

Code:

public class Salary 
{

	public static void main(String[] args) 
	{
		double salary[]={300, 200, 600, 700, 2000, 8000, 800, 800, 900, 6000, 1100};
		int frequency []= new int [11];
		System.out.printf("%10s: %6s:\n","Range", "Frequency");
		for (int range = 0; range < (salary.length); range++)
			++frequency[(int)Math.floor(((salary[range]*(.9)+200)*.01))];

		for (int range1 =2; range1<frequency.length; range1++)
			System.out.printf("$%4d-%4d: %10d\n", range1*100,range1*100+9,frequency[range1]);
	}


}

Error:

Code:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 20
at Salary.main(Salary.java:11)

I know that if i just feed the numbers without doing the math, the application seems to work, but when i start doing the math, it stops working. I'm using the Math.
floor in order to get an integer value, which can then be pushed into the frequency array.

The frequency array should collect the values between 0 and 10 and then print them (as number of people) next to the range of salary.
Thanks

[coco]

Ok, so as the error suggests you are trying to access an array index which is outside the bounds for that array. Take a look at the following code.

Code:

for (int range = 0; range < (salary.length); range++)
{
  //Added this print statement so we can see why we're going out of bounds.
  System.out.println((int)Math.floor(((salary[range]*(.9)+200)*.01)));
  ++frequency[(int)Math.floor(((salary[range]*(.9)+200)*.01))];
}

You declare frequency as an array of size 11; which means the valid indexes for that variable are frequency[0] to frequency[10].
If you run your code with the added print statement and look at the numbers that get printed out you'll see that it prints 4,3,7,8,20 which are the numbers that are computed by (int)Math.floor(((salary[range]*(.9)+200)*.01)) for each iteration of the for loop. The error occurs at the computed value of 20.

If we simplify your code that means you're doing the following in your for loop

Code:

++frequency[4]
++frequency[3]
++frequency[7]
++frequency[8]
++frequency[20]

20 is not a valid index of the frequency array. As I previously stated since the array has a length of 11, trying to access the array at an index greater than 10 will give an array out of bounds error.

This suggests to me that your computation logic is slightly off.

Greetings.