Java - IndexOutOfBoundsException

Question

I'm not a beginner at Java, but nor am I an expert, which is why I am posting this for help/explanation. I've looked in many places across the internet, and there hasn't been an answer I'm looking for.

public class Driver {

public static ArrayList<ArrayList<Integer>> theData; // ArrayList to store the     ArrayList of values
final static int dataSize = 20; // length of the line of data in the inFile

/***
 * Read in the data from the inFile. Store the current line of values
 * in a temporary arraylist, then add that arraylist to theData, then
 * finally clear the temporary arraylist, and go to the next line of 
 * data.
 * 
 * @param inFile
 */
public static void getData(Scanner inFile) {
    ArrayList<Integer> tempArray = new ArrayList<Integer>();
    int tempInt = 0;

    while (inFile.hasNext()) {
        for (int i = 0; i < dataSize; i++) {
            tempInt = inFile.nextInt();
            tempArray.add(tempInt);
        }
        theData.add(tempArray);
        tempArray.clear();
    }
}

/**
 * @param args
 */
public static void main(String[] args) {
    Scanner inFile = null;
    theData = new ArrayList<ArrayList<Integer>>();

    System.out.println("BEGIN EXECUTION");

    try {
        inFile = new Scanner(new File("zin.txt"));
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        getData(inFile);
    }
    System.out.println(theData.get(5).get(5)); // IndexOutOfBoundsException here
    System.out.println("END EXECUTION");
  }

}

I get an IndexOutOfBoundsException where I label it at. The interesting thing here is that when I was trying to figure this out, I tested to see if the method getData was working correctly, so as the method was iterating in the while loop in getData I printed out the size of the array-theData, AND the size of the arrays in the array theData, and what do you know, it returned a correct size and value. So basically when getData is called on, it works correctly and stores the values, but when I try to call on the values in Main, There is no values in the ArrayList.

I have a feeling this has something to do with when I clear the tempArray I used to add to theData. Any help will be great!

Thanks

score 4 · Accepted Answer · answered Sep 25 '13 at 00:48

4

In this code

theData.add(tempArray);
tempArray.clear();

the variable tempArray is a reference to an ArrayList object. You add that reference to the theData ArrayList. When you call clear() on it, you're clearing the same object whose reference you passed to theData. Instead of calling clear() just initialize a new ArrayList.

answered Sep 25 '13 at 00:48

Sotirios Delimanolis

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Thanks! Stupid mistake by me. The only reason I did it this way is because I did it this way for a similar project for C++(which allows you to do this). – Sep 25 '13 at 00:57
@CraiGreen You're welcome. Take a few minutes to read [Is Java pass-by-reference](http://stackoverflow.com/questions/40480/is-java-pass-by-reference). Also, please consider accepting the answer if it covered everything. – Sotirios Delimanolis Sep 25 '13 at 01:00
1

I did - just had to wait a few minutes for StackOverflow to let me. – Sep 25 '13 at 01:04

Java - IndexOutOfBoundsException

1 Answers1