117 lines
4.5 KiB
HTML
117 lines
4.5 KiB
HTML
<title>RELEASE NOTES: COLLECTIONS 2.0</title>
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<center><h2>RELEASE NOTES: COLLECTIONS 2.0</h2></center>
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<center><h3>NEW COLLECTIONS AND COMPARATORS</h3></center>
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<p>Collections 2.0 includes a significant number of new collections, in addition to several
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useful Comparator classes.</p>
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<p>These collections are new to Collections 2.0:</p>
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<ul>
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<li><strong>Bag</strong> - A Collection that keeps a count of its members of the same
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type, using <code>hashCode</code> to check for equality. Suppose
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you have a Bag that contains <code>{a, a, b, c}</code>. Calling
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getCount on <code>a</code> would return 2, while calling
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uniqueSet would return <code>{a, b, c}</code>. <i>Note: this is an
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interface with several implementations.</i></li>
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<li><strong>DoubleOrderedMap</strong> - Red-Black tree-based implementation of Map.
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This class guarantees
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that the map will be in both ascending key order and ascending
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value order, sorted according to the natural order for the key's
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and value's classes.</li>
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<li><strong>FilterListIterator</strong> - A proxy <code>ListIterator</code> which
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takes a <code>Predicate</code> instance to filter
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out objects from an underlying <code>ListIterator</code>
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instance. Only objects for which the specified
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<code>Predicate</code> evaluates to <code>true</code> are
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returned by the iterator.</li>
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<li><strong>HashBag</strong> - An implementation of <strong>Bag</strong> that is backed by a
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HashMap.</li>
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<li><strong>MultiMap</strong> - This is simply a Map with slightly different semantics.
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Instead of returning an Object, it returns a Collection.
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So for example, you can put( key, new Integer(1) );
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and then a Object get( key ); will return you a Collection
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instead of an Integer. This is an interface implemented
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by <strong>MultiHashMap</strong>.</li>
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<li><strong>SequencedHashMap</strong> - A map of objects whose mapping entries are
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sequenced based on the order in
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which they were added.</li>
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<li><strong>SortedBag</strong> - A type of <strong>Bag</strong> that maintains order among its unique
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representative members</li>
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<li><strong>TreeBag</strong> - An implementation of <strong>Bag</strong> that is backed by a
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TreeMap. Order will be maintained among the unique representative
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members.</li>
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</ul>
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<p>These are the new Comparator classes:</p>
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<ul>
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<li><strong>ComparableComparator</strong> - A Comparator that compares Comparable objects.
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This Comparator is useful, for example,
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for enforcing the natural order in custom implementations
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of SortedSet and SortedMap.</li>
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<li><strong>ComparatorChain</strong> - ComparatorChain is a Comparator that wraps one or
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more Comparators in sequence. The ComparatorChain
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calls each Comparator in sequence until either 1)
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any single Comparator returns a non-zero result
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(and that result is then returned),
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or 2) the ComparatorChain is exhausted (and zero is
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returned). This type of sorting is very similar
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to multi-column sorting in SQL, and this class
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allows Java classes to emulate that kind of behaviour
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when sorting a List.</li>
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<li><strong>ReverseComparator</strong> - Reverses the order of another comparator.</li>
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</ul>
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<center><h3>CHANGED COLLECTIONS</h3></center>
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These classes have changed since Collections 1.0:
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<p><u>ArrayIterator</u></p>
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<p><i>Bugs fixed:</i></p>
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<ul>
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<li>ArrayIterator can now iterate over arrays of primatives</li>
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</ul>
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<p><u>LRUMap</u></p>
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<p>LRUMap has been reimplemented as a subclass of
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SynchronizedHashMap. The new implementation of
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LRUMap should be faster, and it also offers true LRU
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capabilities; now any get(Object) or
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put(Object,Object) from this collection
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promotes the key to the Most Recently Used position.</p>
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<p><i>LRUMap 2.0 compatibility changes:</i></p>
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<ul>
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<li>LRUMap can no longer be cast to a HashMap.</li>
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<li>The removeLRU() method now has a different
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signature, and is no longer public. Instead, use
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remove(getFirstKey()).</li>
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<li>"Externalized" LRUMap 1.0 Objects cannot be
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read by LRUMap 2.0.</li>
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</ul>
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<p><i>New features:</i></p>
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<ul>
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<li>True LRU algorithm.</li>
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<li>New methods from SequencedHashMap superclass.</li>
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<li>processRemovedLRU(Object key, Object value) method
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allows subclasses to perform custom actions on
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keys and values that are expunged from the Map.</li>
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</ul>
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<p><i>Bugs fixed:</i></p>
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<ul>
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<li>calling setMaximumSize(int) will remove excess LRUs
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when the current size of the Map exceeds the new
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maximum size</li>
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</ul>
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