Question

So I have this loop in my code that needs two separately working Iterators. However, when it tries to use rbIterator.next(), java throws a ConcurrentModificationException. How do I stop that from happening?
Thanks

Iterator<Road> raIterator = roads.listIterator(0); //I also tried .iterator(), with no avail
while(raIterator.hasNext()){
    Road ra = raIterator.next();
    Iterator<Road> rbIterator = roads.listIterator(0);
    while(rbIterator.hasNext()){
        Road rb = rbIterator.next();
        //snipped code that adds a road to the list
        roads.add(xyz);
    }
}

Answer 1

You can’t add items to most standard implementations of List while iterating over them, unless you create an implementation that allows it!

ArrayList does not, however, see javadoc. Nor do most* (perhaps all) of the Java Collections Frameworks List implementations.

A solution would be to create a new list, temp, before iterating, add elements to temp while you iterate, and then add all of the elements in temp to the first.

Edit: used addAll(temp), thanks @Michael Easter

List<Road> temp = new ArrayList<Road>();

for(Road ra : roads){
    for (Road rb : roads){
        temp.add(xyz);
    }
}

roads.addAll(temp);