Enhancements to Java Collections API

[Jonathan Bluett-Duncan]

Hi John,

I'm not sure about most of the suggestions you've made, especially the
Bidi* ones, but I understand that something like your suggestion for an
enhanced `Optional<V> getIfPresent(K key)` is (or was) being investigated
by Mr. Goetz himself and other people over at Project Valhalla
<http://openjdk.java.net/projects/valhalla/>. However, I can't seem to find
the archived email where it was announced...

Kind regards,
Jonathan

On 29 November 2016 at 20:13, John Platts <john_platts at hotmail.com> wrote:

> There are many features that are missing from the Java Collections API
> that should be added to the Java Collections API, including the following:
>
>   *   Bidirectional iterators for collections other than lists
>      *   New interfaces
>         *   BidiIterator - bidirectional iterator
>            *   extended by ListIterator interface
>            *   has hasPrevious() and previous() methods
>         *   ReverseIterable - reverse iterable
>            *   extends Iterable
>            *   extended by List, Deque, NavigableSet, and BidiIterable
>            *   has descendingIterator() and reverseForEach(Consumer<?
> super T>) methods
>         *   BidiIterable - bidirectional iterable
>            *   extends ReverseIterable
>            *   bidiIterator() returns a BidiIterator
>            *   bidiIteratorFromEnd() returns a BidiIterator that is
> positioned just past the last element in the collection
>            *   extended by List, BidiIterableCollection, BidiIterableSet,
> BidiIterableNavigableSet, and BidiIterableDeque
>         *   BidiIterableCollection - bidirectional iterable collection,
> extends BidiIterable and Collection
>            *   extended by List, BidiIterableSet,
> BidiIterableNavigableSet, and BidiIterableDeque
>            *   default implementation of bidiIterator() method added to
> the java.util.List interface that delegates to java.util.List.listIterator()
>            *   default implementation of bidiIteratorFromEnd() method
> added to the java.util.List interface that delegates to
> java.util.List.listIterator(size())
>         *   BidiIterableSet - bidirectional iterable set, extends
> BidiCollection and Set
>         *   BidiIterableNavigableSet - bidirectional iterable navigable
> iterable set, extends BidiIterableSet and NavigableSet
>            *   subSet(), headSet(), and tailSet() all return
> BidiIterableNavigableSet instances
>         *   BidiIterableDeque - bidirectional iterable deque, extends
> BidiCollection and Deque
>         *   BidiIterableMap - bidirectional iterable map
>            *   extends Map
>            *   keySet() and entrySet() return BidiIterableSet
>            *   values() returns BidiCollection
>            *   has reverseForEach(BiConsumer<? super K, ? super V>) method
>         *   BidiIterableNavigableMap - bidirectional iterable navigable map
>            *   extends BidiIterableMap and NavigableMap
>            *   keySet(), navigableKeySet(), and descendingKeySet() all
> return BidiNavigableSet
>            *   entrySet() returns BidiIterableSet
>            *   values() returns BidiCollection
>            *   subMap(), headMap() and tailMap() all return
> BidiIterableNavigableMap instances
>      *   BidiIterableDeque interface implemented on java.util.ArrayDeque,
> java.util.concurrent.ConcurrentLinkedDeque, java.util.concurrent.LinkedBlockingDeque,
> and java.util.LinkedList
>      *   BidiIterableSet interface implemented on java.util.LinkedHashSet,
> java.util.TreeSet, and java.util.concurrent.ConcurrentSkipListSet
>      *   BidiIterableNavigableSet interface implemented on
> java.util.TreeSet and java.util.concurrent.ConcurrentSkipListSet
>      *   BidiIterableMap interface implemented on java.util.LinkedHashMap,
> java.util.TreeMap, and java.util.concurrent.ConcurrentSkipListMap
>      *   BidiIterableNavigableMap interface implemented on
> java.util.TreeMap and java.util.concurrent.ConcurrentSkipListMap
>   *   Pollable interface
>      *   Extended by the Queue, Deque, and NavigableSet interfaces
>      *   Also implemented by the java.lang.ref.ReferenceQueue class
>      *   Contains the poll() method, which is already defined by the Queue
> and Deque interfaces
>   *   BidiPollable interface
>      *   Extends the Pollable interface
>      *   Extended by the Deque and NavigableSet interfaces
>      *   Contains the pollFirst() and pollLast() methods, which are
> already defined in both the Deque and NavigableSet interfaces
>   *   Navigable versions of java.util.EnumMap and java.util.EnumSet
>      *   Option #1: Implement the NavigableMap interface on top of
> java.util.EnumMap and java.util.EnumSet
>      *   Option #2: Implement separate java.util.NavigableEnumMap and
> java.util.NavigableEnumSet classes that behave similarly to the existing
> java.util.EnumMap and java.util.EnumSet classes, except that the
> java.util.NavigableEnumMap class has the functionality of the
> java.util.NavigableMap interface and that the java.util.NavigableEnumSet
> class has the functionality of the java.util.NavigableSet interface.
>      *   Under both options, the comparator() method of the navigable
> versions of EnumMap and EnumSet would return null
>      *   Navigable versions of EnumMap and EnumSet are possible since all
> enum types implement the Comparable interface
>   *   New enhanced map and set implementations
>      *   Support for hash maps and hash sets with custom hashcode function
> and custom equality predicate
>      *   Enhanced map interface that defines a Optional<V> getIfPresent(K
> key) method that returns the following:
>         *   A non-empty optional if the key is contained in the map and
> the value is non-null
>         *   An empty optional if the key is contained in the map, but the
> value is null
>         *   null if the map does not contain key
>
> Will these enhancements ever make it into Java SE 10 or Java SE 11?
>
>   *
>