Java Developers Book: ConcurrentAcessModification

Sunday, 27 July 2014

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");

       }
    }

}