Java not recognizing elements in ArrayList?

Question

I have a program where I make an arraylist to hold some cab objects. I keep getting an error that what I get from the message is that java does not recognize that the arraylist has objects in it. This is the error that I am getting.

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 20, Size: 20
at java.util.ArrayList.rangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at edu.Tridenttech.MartiC.app.CabOrginazer.main(CabOrginazer.java:48)

This is the code that i am trying to get to work

public class CabOrginazer {

private static List<CabProperties> cabs = new ArrayList<CabProperties>();
private static  int count = 0;
private static boolean found = false;


public void cabOrginazer() 
{

}

public static void main(String[] args) {
    // TODO Auto-generated method stub
    CabRecordReaper reaper = new CabRecordReaper("C:/CabRecords/September.txt");
    CabProperties cabNum;

    for(int i = 0; i < 20; i++)
    {
        cabNum = new CabProperties();
        cabs.add(cabNum);
    }
    while(reaper.hasMoreRecords())
    {
            CabRecord file = reaper.getNextRecord();
            for(int j = 0; j < cabs.size(); j++)
            {
                if(cabs.get(j).getCabID() == file.getCabId())
                {
                    found = true;
                    cabs.get(j).setTypeAndValue(file.getType(), file.getValue(), file.getPerGallonCost());
                    cabs.get(j).setDate(file.getDateString());
                    break;
                }

            }

            if(found == false)
            {
                cabs.get(count).setCabId(file.getCabId());
                count++;
            }
            /*for(CabProperties taxi : cabs)
            {
                if(taxi.getCabID() == file.getCabId())
                {
                    found = true;
                    taxi.setTypeAndValue(file.getType(), file.getValue(), file.getPerGallonCost());
                    taxi.setDate(file.getDateString());
                    break;
                }


            }*/

    }


    for(CabProperties taxi : cabs)
    {
        System.out.print("cab ID: " + taxi.getCabID());
        System.out.print("\tGross earning: " +  taxi.getGrossEarn());
        System.out.print("\tTotal Gas Cost: " + taxi.getGasCost());
        System.out.print("\tTotal Service Cost: " +  taxi.getServiceCost());
        System.out.println();

    }


}

}

line 48 is the inside of that if statement where it says cabs.get(count).setCabId(file.getCabId()); with the little knowledge I have of Java. Java should know that there are elements inside of cabs and I should be able to set that id of the cab. What can cause Java not to recognize that the arraylist is populated?

Jon Skeet · Accepted Answer · 2014-10-01 13:05:57Z

7

The list isn't populated with an element at item count. Look at the exception: you've got 20 elements in the list, so the valid indexes are 0 to 19 inclusive. You're asking for record 20 (i.e. the 21st record). That doesn't exist.

It sounds like your block should be something like:

if (!found)
{
    CabProperties properties = new CabProperties();
    properties.setCabId(file.getCabId());
    // Probably set more stuff
    cabs.add(properties);
}

You may well be able to get rid of the count variable entirely - and your initial population of the list with dummy properties. It's very odd to populate a list like that to start with - that's typically something you do with an array which has a fixed size. One of the main benefits of using a List such as ArrayList is that it's dynamically sized.

answered Oct 1, 2014 at 13:05

Jon Skeet

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Comments

rolfl · Accepted Answer · 2014-10-01 13:06:21Z

4

Java is recognizing the members just fine. You have 20 members in the array, indexed from index 0 through index 19.

You are asking for index 20, which does not exist.

The loop for:

while(reaper.hasMoreRecords())

must be running many more times than you expect, and your data is hitting the found == false if condition (which you can just say if (!found) { ... ) many times, and on the 21st time it fails with the index-out-of-bounds exception.

You should figure out how to use your debugger too.

answered Oct 1, 2014 at 13:06

rolfl

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