Collections

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Iterable and Iterators

Items cannot be added to a collection directly while iterating through the collection in a for-each loop or through the collection’s iterator; doing so will throw a ConcurrentModificationException at runtime. The appropriate way to modify the structure of a collection that is undergoing iteration is through the iterator.remove() method.


// Reference Collections1 p. 174

// throws ConcurrentModificationException
for (Task t : tuesdayTasks) {
if (t instanceof PhoneTask) {
tuesdayTasks.remove(t);
}
}
// throws ConcurrentModificationException
for (Iterator it = tuesdayTasks.iterator() ; it.hasNext() ; ) {
Task t = it.next();
if (t instanceof PhoneTask) {
tuesdayTasks.remove(t);
}
}
for (Iterator it = tuesdayTasks.iterator() ; it.hasNext() ; ) {
Task t = it.next();
if (t instanceof PhoneTask) {
it.remove();
}
}


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Synchronized Collections

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java.util.Collections class

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References
Collections1: Java Generics and Collections. Maurice Naftalin and Philip Wadler. O’Reilly Media 2007.