- Type Parameters:
T - the type contained
- All Implemented Interfaces:
- Iterable<T>, Collection<T>, Set<T>
- Enclosing class:
- CollectionFactory
public static class CollectionFactory.ConditionalCopySet<T>
extends Object
implements Set<T>
a set implementation that uses a delegate collection for all read-only
operations and makes a copy if changes are attempted. Useful for cheap
defensive copies: no costly rehashing on the original collection is made
unless changes are attempted. Changes are not mirrored back to the
original collection, although changes to the original set BEFORE changes
to the copy are reflected in the copy. If the source collection is not
supposed to change, then this collection behaves just like a regular
defensive copy; if the source collection can change, then this collection
should be built from a cheap copy of the original collection. For
example, if the source collection is a set, it can be copied into a list;
the cost of the copy operation from set to list is approximately 1/3 of
the cost of copying into a new HashSet. This is not efficient if the most
common operations performed on the copy are contains() or containsAll(),
since they are more expensive for lists wrt sets; a counter for these
calls is maintained by the collection, so if a large number of
contains/containsAll calls takes place, the delegate is turned into a
regular set. This implementation is not threadsafe even if the source set
is: there is no lock during the copy, and the new set is not threadsafe.