Re: Ranking

From:
"Crouchez" <blah@bllllllahblllbllahblahblahhh.com>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 28 Aug 2007 18:04:11 GMT
Message-ID:
<vsZAi.90667$p7.67415@fe2.news.blueyonder.co.uk>
"Lew" <lew@lewscanon.com> wrote in message
news:v8ednT0Mpb5XPU7bnZ2dnUVZ_hOdnZ2d@comcast.com...

Crouchez wrote:

Concurrent means multiple threads though doesn't it?


Lew wrote:

<http://java.sun.com/javase/6/docs/api/java/util/ConcurrentModificationException.html>

Note that this exception does not always indicate that an object has
been
concurrently modified by a /different/ thread.

(emphasis in the original)


<sscce>
/* ConcurrentModifier
 * $Id$
 */
package testit;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/** Cause a <code>ConcurrentModificationException</code>.
 */
public class ConcurrentModifier
{
    /** Cause a <code>ConcurrentModificationException</code>.
     * @param args <code>String []</code> program arguments.
     */
    public static void main( String [] args)
    {
        List <String> strangs = new ArrayList <String> ();
        strangs.add( "first" );
        strangs.add( "second" );
        strangs.add( "remove" );
        strangs.add( "last" );

        String val;

        Iterator <String> iter = strangs.iterator();
        if ( iter.hasNext() )
        {
            val = iter.next();
            System.out.println( val );
            System.out.println( "" );
        }

        if ( iter.hasNext() )
        {
            if ( strangs.remove( "remove" ) )
            {
                System.out.println( "Removed" );
            }
            else
            {
                System.out.println( "Not removed" );
            }
            System.out.println( "" );
        }

        while ( iter.hasNext() )
        {
            val = iter.next(); // line 50
            System.out.println( val );
            System.out.println( "" );
        }
        System.out.println( "out of elements" );
    }
}
</sscce>

Output:

first

Removed

Exception in thread "main" java.util.ConcurrentModificationException
        at
java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
        at java.util.AbstractList$Itr.next(AbstractList.java:343)
        at testit.ConcurrentModifier.main(ConcurrentModifier.java:50)

--
Lew


That's it - it wasn't a different thread - items were being removed inside
the iterator.. doh

What's the best way to do remove while in the loop? Is it to store the
objects temporarily in an array and remove after or is there a built-in api
way?

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