IndexOutOfBounds Exception

[James Allen A.]

The code is pretty messy at this point so my apologies, but I'm running into an IndexOutOfBounds Exception:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 2, Size: 2
	at java.util.ArrayList.rangeCheck(ArrayList.java:604)
	at java.util.ArrayList.get(ArrayList.java:382)
	at CointingCoins.main(CointingCoins.java:65)

Here's my code. It references line 65 where I'm trying to create a loop to go through each position in ArrayList coins.

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Collections;
import java.util.Random;

public class CointingCoins {
	
	public static void main(String[] args) {
		
		double getcoinctrl = 0;
		int ordcoincount = 1;
		double coinreturn;
		String morecoins;
		double changeamount = 0;
		
		ArrayList<Double> coins = new ArrayList<Double>();
		ArrayList<Double> coinsDenom = new ArrayList<Double>();
	
		do {
	
		System.out.println("Please enter the value of the " + ordcoincount + " coin: ");
		
		Scanner myScanner = new Scanner(System.in);
		
		coinreturn = myScanner.nextDouble();
		
		coins.add(coinreturn);
		
		System.out.println("Would you like to add another coin value? (Y/N)");
		
		morecoins = myScanner.next();
		
		morecoins.toLowerCase();
		
		ordcoincount++;
		getcoinctrl++;
		
		} while ("y".equals(morecoins) || "yes".equals(morecoins));  //Fix to close negative return gap
		
		
		System.out.println("Please enter the change amount in cents (no decimal): ");
			
		Scanner myScanner2 = new Scanner(System.in);
			
		changeamount = myScanner2.nextDouble();
		
		Collections.sort(coins);
		
		double denomreturn;
		
		for (int i = 0; i < coins.size(); i++) {
			denomreturn = Math.floor(changeamount / coins.get(i));
			coinsDenom.add(denomreturn);
		}
		
		//ListIterator<Float> listIterator = coins.listIterator();
		//ListIterator<Float> listIterator2 = coinsDenom.listIterator();
		
		long arraysum;
		double exactchangecnt = 0;
		double subtotal = 0;
		
		for (int i = coins.size(); i >= 0; i--) {
			
			subtotal = subtotal + (coins.get(i));
			/*while (listIterator.hasNext()) {
				arraysum = (arraysum * listIterator.next());
			
				if (arraysum == changeamount) {
				exactchangecnt++;
				}
			}*/
		}
		
		System.out.println(subtotal);
		System.out.println(coins);
		System.out.println(coinsDenom);
		
		
		
		/* public static String getOrdinalFor(int value) {
			 int tenRemainder = value % 10;
			 switch (tenRemainder) {
			  case 1:
			   return "st";
			  case 2:
			   return "nd";
			  case 3:
			   return "rd";
			  default:
			   return "th";
			 }
			}
			*/
	}

}

[James Allen A.]

Scratch that. I had a misunderstanding of what ArrayList.size() returns. My mistake was that I called on a position after the place where the final position in the array occurs. Hence the "out of range" exception. Got it now.

[Tim Cooke]

So this is the offending bit of code:

for (int i = coins.size(); i >= 0; i--) {  
            subtotal = subtotal + (coins.get(i));  
        }

Let's say your coins has 2 items in it. coins.size() will return 2 which means you're then going on to do coins.get(2). But array indexes start at 0 which means an array with two things in it have indexes of 0 and 1 which is where your IndexOutOfBoundsException comes from as there's no element at index 2.

Unless there's a particular reason for looping in reverse, the common syntax for a for loop is

for (int i = 0; i < coins.size(); i++) {
  Double coin = coins.get(i);
}

But if you must go in reverse then:

for (int i = coins.size() - 1; i >= 0; i--) {
  Double coin = coins.get(i);
}

Or using the foreach notation:

for (Double coin: coins) {
  // coin is available here
}

As an additional piece of advice. It is never a great idea to use basic numeric types for dealing with currency in an application as you'll always be at the mercy of implicit casting and rounding errors. A headache waiting to happen. Consider creating your own Money object using the Quantity Pattern

[Ivan Jozsef Balazs]

This won't work. size() is one past the last element index:

for (int i = coins.size(); i >= 0; --i) {  
  Double coin = coins.get(i);  
} 

You have to subtract one:

for (int i = coins.size() - 1; i >= 0; --i) {  
  Double coin = coins.get(i);  
} 

[Tim Cooke]

Ivan Jozsef Balazs wrote:This won't work. size() is one past the last element index:

Rookie mistake. Sorry about that and thanks for pointing it out. I've corrected my original post.