Iteration, multithread access, cuncurrenthashmap, swing, Strange Error

Question

Hi,
Lets start with the error:
Exception in thread "Thread-2" java.lang.IllegalStateException
     at java.util.concurrent.ConcurrentHashMap$HashIterator.remove(Unknown Source)
     at DrawFrame$allthread.run(DrawFrame.java:569)
     at java.lang.Thread.run(Unknown Source)Next lets look at the code:
                    Iterator<Rectangle> hr = rectangles.values().iterator();
                                   while (hr.hasNext()) {
                                        Rectangle rh = hr.next();
                                                                     if (somecondition){
                                                                         hr.remove();
                                                        }So apparently it looks like I'm trying to remove a rectangle, this works fine for a while, but then will randomly break at an unexpected time. Anyone got any advice? I think the error should be apparent. By the way, this is hashmap is getting used by seperate threads... but it is a cuncurrenthashmap.
Whats goin on?
Nate

Answer 1

Myth shot down in flames...
package forums;
import java.util.Iterator;
import java.util.Map;
import java.util.HashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ConcurrentHashMap;
class ConcurrentHashMapPutAllContainingNullTest
  public static void main(String[] args) {
    try {
      Map<Integer,String> map = new HashMap<Integer,String>();
      map.put(1, "ONE");
      map.put(2, null);
      map.put(3, "THREE");
      ConcurrentMap<Integer,String> cache = new ConcurrentHashMap<Integer,String>();
      cache.putAll(map); // this is line 19
    } catch (Exception e) {
      e.printStackTrace();
produces
C:\Java\home\src\forums>"C:\Program Files\Java\jdk1.6.0_07\bin\java.exe" -Xms512m -Xmx1024m -enableassertions -cp C:\Java\home\classes; forums.ConcurrentHashMapPutAllContainingNullTest
java.lang.NullPointerException
        at java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:881)
        at java.util.concurrent.ConcurrentHashMap.putAll(ConcurrentHashMap.java:909)
        at forums.ConcurrentHashMapPutAllContainingNullTest.main(ConcurrentHashMapPutAllContainingNullTest.java:19)