These collections are new to Collections 2.0:

• Bag - A Collection that keeps a count of its members of the same type, using hashCode to check for equality. Suppose you have a Bag that contains {a, a, b, c}. Calling getCount on a would return 2, while calling uniqueSet would return {a, b, c}. Note: this is an interface with several implementations.
• DoubleOrderedMap - Red-Black tree-based implementation of Map. This class guarantees that the map will be in both ascending key order and ascending value order, sorted according to the natural order for the key's and value's classes.
• FilterListIterator - A proxy ListIterator which takes a Predicate instance to filter out objects from an underlying ListIterator instance. Only objects for which the specified Predicate evaluates to true are returned by the iterator.
• HashBag - An implementation of Bag that is backed by a HashMap.
• MultiMap - This is simply a Map with slightly different semantics. Instead of returning an Object, it returns a Collection. So for example, you can put( key, new Integer(1) ); and then a Object get( key ); will return you a Collection instead of an Integer. This is an interface implemented by MultiHashMap.
• SequencedHashMap - A map of objects whose mapping entries are sequenced based on the order in which they were added.
• SortedBag - A type of Bag that maintains order among its unique representative members
• TreeBag - An implementation of Bag that is backed by a TreeMap. Order will be maintained among the unique representative members.

ArrayIterator

Bugs fixed:

• ArrayIterator can now iterate over arrays of primatives

LRUMap

LRUMap has been reimplemented as a subclass of SynchronizedHashMap. The new implementation of LRUMap should be faster, and it also offers true LRU capabilities; now any get(Object) or put(Object,Object) from this collection promotes the key to the Most Recently Used position.

LRUMap 2.0 compatibility changes:

• LRUMap can no longer be cast to a HashMap.
• The removeLRU() method now has a different signature, and is no longer public. Instead, use remove(getFirstKey()).
• "Externalized" LRUMap 1.0 Objects cannot be read by LRUMap 2.0.

New features:

• True LRU algorithm.
• New methods from SequencedHashMap superclass.
• processRemovedLRU(Object key, Object value) method allows subclasses to perform custom actions on keys and values that are expunged from the Map.

Bugs fixed:

• calling setMaximumSize(int) will remove excess LRUs when the current size of the Map exceeds the new maximum size