ConcurrentAcessModification Exception Java

ConcurrentAcessModification Exception Java This exception does not normally have anything to do with synchronization - it is normally thrown if a Collection is modified while an Iterator is iterating through it. AddAll methods may use an iterator - and its worth noting that the posh foreach loop iterates over instances of Iterator too. Example -  import java.util.HashMap; import java.util.Iterator; import java.util.Set; public class Test{         public static void main(String[] args) {         HashMap map = new HashMap();         map.put(1,"1");         map.put(2,"2");         map.put(3,"3");         map.put(4,"4");         map.put(5,"5");         map.put(6,"6");         Set keyset = map.keySet();         Iterator iterator = keyset.iterator();         while(iterator.hasNext()){           System.out.println(map.get((Integer)iterator.next()));           // Here you will get java.lang.ConcurrentAccessModification Exception.             map.put(6,"6");             map.put(7,"7");                    }     } }