current modification exception

[Abigail Decan]

import java.util.*;
public class MyList
{
private LinkedList<String> l;
private ListIterator<String> i;
public MyList()
{
l = new LinkedList<String>();
i = l.listIterator();
}
public void add(String s)
{
l.add(s);
}
public String getNext()
{
String rtn;
if(i.hasNext())
{
rtn = i.next();
}
else
{
// return first element
rtn = l.get(0);
// reset next function
ListIterator<String> i2 = l.listIterator();
this.i = i2;
}
return rtn;
}
public static void main(String[] args)
{
MyList l = new MyList();
l.add("spring");
l.add("summer");
l.add("fall");
l.add("winter");
for(int i = 1; i <= 5; ++i)
{
System.out.println(l.getNext());
}
}
}

this gave me

Exception in thread "main" java.util.ConcurrentModificationException
at java.util.LinkedList$ListItr.checkForComodification(Unknown Source)
at java.util.LinkedList$ListItr.next(Unknown Source)
at MyList.getNext(MyList.java:23)
at MyList.main(MyList.java:49)

i don't understand why.

apparently the line

rtn = i.next();

is the problem.
but i'm not modifying my linked list with this code.

[Daryl Cofer]

When your iterator calls the next method, it checks to see if its expectedModCount is equal to the list's modCount it is iterating over. If these numbers don't match, the iterator thinks that the list has been modified and it throws the exception that you received.

[Stephan van Hulst]

To add to what Daryl already said, the reason these numbers don't match, is because you're initializing i with an iterator and you add values to the list before using it.

It's usually a bad idea to keep references to iterators outside of a method scope. The only time I've needed this myself was when I was implementing an iterator that traverses trees depth-first, and kept a reference to a recursive iterator.

[Daryl Cofer]

The LinkedList class already has a built in iterator anyway, so why would you want to make a new one?
If you want to go through the elements in your MyList class, you might want to look into making it iterable by implementing the Iterable interface.