6407460: provide Collections helper methods for new interfaces in JDK 1.6 (original) (raw)

David Schlosnagle schlosna at gmail.com
Sun Jan 16 23:42:50 UTC 2011

Hello core-lib-devs,

The recent discussions around Objects.nonNull prompted me to create a patch (attached) to add the methods below to java.util.Collections for consistency with existing methods. According to the Annotated Outline of Collections Framework [1] [2], the unmodifiable methods for some of the newer Collection types (Queue, Deque, NavigableSet, NavigableMap) seem to be missing, and the empty methods for many new and old interfaces (SortedSet, NavigableSet, Queue, Deque, SortedMap, NavigableMap) that would also be nice to have.

In some of my projects, I could really benefit from having these additional Collections.empty* and Collections.unmodifiable* helper methods to simplify my code. In many cases these are places where internally a null collection is used to allow for lazy initialization, but the externally exposed APIs would always return an empty or unmodifiable collection via a simple toUnmodifiable utility method (where to include those in the JDK is probably a whole separate argument). Previously the interfaces exposed in my APIs were often List, Map, or Set, but more recently I've also been using SortedMap and SortedSet where applicable, so I've felt a little pain for not having all of the expected methods in Collections. There are of course libraries such as Guava that also provide the majority of these (and much more), but I think it would be nice to have this in the JDK.

There seems to have been some discussion and bug IDs related to some of these methods over the past few years [3] [4] [5] [6], but I'm curious if this is something that would be considered for adding to the Java API, and if so would it be for JDK 1.7 or 1.8 seeing as how Mark indicated 1.7 was feature complete? I look forward to everyone's feedback.

unmodifiableNavigableSet(NavigableSet s)

extends E> it)

unmodifiableListIterator(ListIterator<? extends E> it)

unmodifiableNavigableMap(NavigableMap<K, ? extends V> m)

Here's a little summary of what versions of the JDK contain the various empty and unmodifiable methods, and which are covered by this patch:

Interface empty* unmodifiable*

Collection n/a 1.2+ Set 1.5+ 1.2+ List 1.5+ 1.2+ Queue patch patch Deque patch patch Map 1.5+ 1.2+ SortedSet patch 1.2+ SortedMap patch 1.2+ NavigableSet patch patch NavigableMap patch patch BlockingQueue ? ? TransferQueue ? ? BlockingDeque ? ? ConcurrentMap ? ? ConcurrentNavigableMap ? ? Iterator 1.7+ patch ListIterator 1.7+ patch

I've updated a few of the jtreg tests as initial sanity checks, but if this patch were to be considered I'd want to expand those a bit more. I haven't yet addressed the missing synchronized (Queue, Deque, NavigableSet, NavigableMap), checked (Queue, Deque, NavigableSet, NavigableMap), singleton (SortedSet, NavigableSet, Queue, Deque, SortedMap, NavigableMap) methods. Also, I haven't created analogous methods for any of the java.util.concurrent interfaces as I'm not sure that these methods necessarily make sense for those types.

P.S. I submitted a signed OCA to sun_ca at sun.com earlier today, but I'm assuming it will take a while to be added to https://sca.dev.java.net/CA_signatories.htm since it is a holiday weekend here in the USA.

References: [1]: http://download.oracle.com/javase/6/docs/technotes/guides/collections/reference.html [2]: http://download.java.net/jdk7/docs/technotes/guides/collections/reference.html [3]: 4834905: Support read-only Iterator, i.e., without remove(): http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4834905 [4]: 5030930: JDK1.5 The method Collections.unmodifiableQueue(Queue<? extends T>) is missing: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5030930 [5]: 6407460: (coll) provide Collections helper methods for new interfaces in JDK 1.6: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6407460 [6]: How about Collections.emptySorted[Set|Map] ?: http://markmail.org/message/6u23eysno2mt6ia4 -------------- next part -------------- A non-text attachment was scrubbed... Name: 6407460.patch Type: application/octet-stream Size: 50928 bytes Desc: not available URL: <http://mail.openjdk.java.net/pipermail/core-libs-dev/attachments/20110116/c6149ca9/6407460.patch>

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