Question

HashMap ConcurrentModificationException

Asked by: ycomp

Hi,

What is wrong with my code here?

  private HashMap mappings;

  private void prune() {
    // for every mapping in mappings
    Iterator it = mappings.keySet().iterator();
    while (it.hasNext()) { // for every mapping
      String key = (String) it.next();
      Object o = mappings.get(key);
      if (!(o instanceof ArrayList)) // if not an ArrayList
        mappings.remove(key); // delete mapping
    }
  }

java.util.ConcurrentModificationException
      at java.util.HashMap$HashIterator.nextEntry(HashMap.java:762)
      at java.util.HashMap$KeyIterator.next(HashMap.java:798)
      at com.test.MappingsGrid.prune(MappingsGrid.java:73)

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Asked On
2004-11-13 at 14:08:18ID21205918
Tags

concurrentmodificationexception

,

hashmap

Topic

Java Programming Language

Participating Experts
3
Points
500
Comments
7

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Answers

 

by: petmagdyPosted on 2004-11-13 at 14:28:18ID: 12575978

how do u run this code?
anyway try:
      if (!(o instanceof ArrayList)) // if not an ArrayList
        synchronized(mappings)
{
        mappings.remove(key); // delete mapping
}
........

 

by: objectsPosted on 2004-11-13 at 14:32:36ID: 12575988

>        mappings.remove(key); // delete mapping

that should be:

it.remove();

 

by: objectsPosted on 2004-11-13 at 14:33:23ID: 12575990

you cannot delete entries directly from the map while you are iterating thru it

 

by: CEHJPosted on 2004-11-13 at 14:34:52ID: 12575995

If more than one thread is involved, create your Map thus:

Map synchMappings = Collections.synchronizedMap(mappings);

and then operate on 'synchMappings'

 

by: ycompPosted on 2004-11-13 at 15:20:01ID: 12576149

sorry.. forgot to say it is a single thread.

objects: that's what I was thinking... any ideas how I should do what I want to do.. i.e. delete those mappings w/o throwing an exception?

 

by: ycompPosted on 2004-11-13 at 15:21:18ID: 12576155

objects: sorry I should read more carefully next time.. I'll check out it.remove()

 

by: objectsPosted on 2004-11-13 at 15:30:29ID: 12576186

:)

20120131-EE-VQP-002

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