On Wed, 4 Nov 2020 09:46:32 GMT, Zheka Kozlov <github.com+761899+orio...@openjdk.org> wrote:
>> This change introduces a new terminal operation on Stream. This looks like a >> convenience method for Stream.collect(Collectors.toList()) or >> Stream.collect(Collectors.toUnmodifiableList()), but it's not. Having this >> method directly on Stream enables it to do what can't easily by done by a >> Collector. In particular, it allows the stream to deposit results directly >> into a destination array (even in parallel) and have this array be wrapped >> in an unmodifiable List without copying. >> >> In the past we've kept most things from the Collections Framework as >> implementations of Collector, not directly on Stream, whereas only >> fundamental things (like toArray) appear directly on Stream. This is true of >> most Collections, but it does seem that List is special. It can be a thin >> wrapper around an array; it can handle generics better than arrays; and >> unlike an array, it can be made unmodifiable (shallowly immutable); and it >> can be value-based. See John Rose's comments in the bug report: >> >> https://bugs.openjdk.java.net/browse/JDK-8180352?focusedCommentId=14133065&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14133065 >> >> This operation is null-tolerant, which matches the rest of Streams. This >> isn't specified, though; a general statement about null handling in Streams >> is probably warranted at some point. >> >> Finally, this method is indeed quite convenient (if the caller can deal with >> what this operation returns), as collecting into a List is the most common >> stream terminal operation. > > src/java.base/share/classes/java/util/ImmutableCollections.java line 240: > >> 238: static <E> List<E> listFromTrustedArrayNullsAllowed(Object... >> input) { >> 239: if (input.length == 0) { >> 240: return (List<E>) EMPTY_LIST; > > If we return a `ListN` here, does this mean that > `Stream.of().toList().contains(null)` will throw an NPE? But this is > incorrect because `toList()` returns a null-tolerant List. Yes, good point, we might need to have a null-tolerant empty list. ------------- PR: https://git.openjdk.java.net/jdk/pull/1026
