www.fernstudenten.de

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

public class ArtikelArray {

public static void main(String[] args) {

ArrayList <String> artikel = new ArrayList <String>();
/*String a = null;*/
Iterator <String> iterator = artikel.iterator();

artikel.add("Uhr");
artikel.add("Tasche");
artikel.add("Laptop");
artikel.add("Koffer");
artikel.add("Jacke");

System.out.println(artikel.isEmpty());
System.out.println("\n");

for (int i=0; i<artikel.size(); i++)
System.out.println(artikel.get(i));
System.out.println("\n");

while(iterator.hasNext())
{
System.out.println(iterator.next());
}

artikel.remove("Koffer");
for (int i=0; i<artikel.size(); i++)
System.out.println(artikel.get(i));
System.out.println("\n");

artikel.set(1, "Koffer");
for (int i=0; i<artikel.size(); i++)
System.out.println(artikel.get(i));
System.out.println("\n");

artikel.add(1, "Tasche");
for (int i=0; i<artikel.size(); i++)
System.out.println(artikel.get(i));
System.out.println("\n");

}

}

Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)
at ArtikelArray.main(ArtikelArray.java:28)

The iterators returned by this class's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.