Index Out Of Bounds Exception when trying to read from file into ArrayList

Question

I am trying to read a series of integers from a file into an ArrayList but when accessing numbers.get(0), I get the Out of Bounds Exception, presumably because nothing has been written to the list.

ArrayList<Integer> numbers = new ArrayList<Integer>();

public void Numbers() throws IOException{

  File file = new File("Numbers.txt");
  Scanner inputFile = new Scanner(file);

  while (inputFile.hasNext()){

    numbers.add(inputFile.nextInt());
  }

    inputFile.close();
}

Any help would be greatly appreciated. I can provide more code snippets if needed.

I don't see a line of code that says numbers.get(0). Where is this code? — Code-Apprentice
– Code-Apprentice, Commented Nov 29, 2012 at 0:36
The first token in the file can't be interpreted as an integer. — Kevin
– Kevin, Commented Nov 29, 2012 at 0:40
I call it in another method like: int lowest = numbers.get(0); — Randallsm83
– Randallsm83, Commented Nov 29, 2012 at 0:42

Code-Apprentice · Accepted Answer · 2012-11-29 00:39:12Z

4

One likely problem is that you have declared the method as

public void Numbers() throws IOException

This is a method called Numbers which returns void and throws IOException. Note that this is not a constructor, which you might intend it to be, because you have declared a return type. If you are calling numbers.get(0) in another method of this same class. This Numbers() method is probably not called explicitly if you expect it to be called automatically as a constructor.

answered Nov 29, 2012 at 0:39

Code-Apprentice

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4 Comments

Randallsm83 Over a year ago

I did intend this to be the constructor so it sounds like this is the problem. Now that I have removed the return type I get the error, Error: unreported exception java.io.IOException; must be caught or declared to be thrown.

Randallsm83 Over a year ago

Btw, this is the line im getting the error on: public static void main(String[] args){ Numbers n = new Numbers();

Code-Apprentice Over a year ago

@Randallsm83 You need to do exactly what the error message says: either catch the IOException which your constructor throws or declare main() to throw it.

Randallsm83 Over a year ago

Thank you, I haven't learned that just yet but I am going to right now!

Yogendra Singh · Accepted Answer · 2012-11-29 00:48:50Z

1

I think its trying to read the token as int and comes out with exception. Try this:

try{
   File file = new File("Numbers.txt");
   Scanner inputFile = new Scanner(file);
   while (inputFile.hasNext()){
    String next = inputFile.next();
    try{
        numbers.add(Integer.valueOf(next));
     }catch(NumberFormatException nfe){
       //not a number, ignore it
     }
   }
 }catch(IOException ioe){
      ioe.printStackTrace();
 }

edited Nov 29, 2012 at 0:48

answered Nov 29, 2012 at 0:40

Yogendra Singh

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6 Comments

Randallsm83 Over a year ago

After fixing the constructor format I get the error unreported exception java.io.IOException; must be caught or declared to be thrown as stated above. I have not learned how to catch yet unfortunately. Is this what I need to learn to alleviate this error?

Eng.Fouad Over a year ago

Consider using hasNextInt() and nextInt().

Yogendra Singh Over a year ago

@Randallsm83 Updated the answer with IOException handling. Please put the code inside your constructor and remove the throws IOException from declaration.

Yogendra Singh Over a year ago

@Randallsm83: In addition, please make sure you perform a size check before int lowest = numbers.get(0); otherwise you will again get IndexOutOfBoundException if your constructor couldn't read your file and numbers list wasn't populated.

Randallsm83 Over a year ago

Perfect! I know the problem now is my book didn't touch on catching the exception which is exactly what it need. Thank you everyone so much for the quick help!

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