Java - Exception in thread “main” java.util.ConcurrentModificationException

Question

Is there any way I can modify the HashMap values of a particular key while iterating over it?

A sample program is given below:

public st         


        

Answer 1

The problem in the code your presented isn't modifying the HashMap, it's modifying the ArrayList while iterating it. You can avoid this exception if you use ar's ListIterator instead of using an enhanced for loop:

for (ListIterator i = ar.listIterator(); i.hasNext(); i.next()) {
    i.add("hello");
}