/*
 * This example shows the wrong and right way to remove items from a
 * LinkedList or similar structure.
 *
 * The problem is one of using an Iterator over a structure while items
 * are being removed from the structure itself.
 */

package linkedlistillustration;

import java.util.LinkedList;


/**
 *
 * @author Robert Keller
 */
public class Main
{

    public static void main(String[] args)
    {

        LinkedList L = new LinkedList<Integer>();

        L.add(2);
        L.add(3);
        L.add(4);
        L.add(5);

// Wrong way to remove even items from the list L:
//
//        for( Object i: L)          // This is an implied iterator.
//          {
//            if( ((Integer)i).intValue() % 2 == 0 )
//              {
//                L.remove(i);
//              }
//          }
//
// The above will not work. It will produce the following runtime exception:
//        Exception in thread "main" java.util.ConcurrentModificationException
//        at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:761)
//        at java.util.LinkedList$ListItr.next(LinkedList.java:696)
//        at linkedlistillustration.Main.main(Main.java:31)
 
// This is the correct way to remove selected items.

        // First make a separate list of the items to be removed.

        LinkedList Removal = new LinkedList<Integer>();

        for( Object i: L)
          {
            if( ((Integer)i).intValue() % 2 == 0 )
              {
                Removal.add(i);
              }
          }

        // Then iterate over the list of items to be removed and remove
        // each individually from the original list.
        // Here we are NOT ITERATING over the original list, so
        // concurrent removal is not a problem.

        for( Object i: Removal)
          {
            L.remove(i);
          }

        System.out.println(L);
    }

}