On 10/31/17 11:24 AM, Roger Riggs wrote:
Hi Stuart,
Collection.java:
The mix of "should" and "must" in Collection.java can be confusing.
Typically "should" is interpreted as "must" from a conformance point of view.
"Must" is a requirement, and "should" is a recommendation to implementors, and
advice to clients that some property often but doesn't necessarily hold.
For example,
147 * <p>An <i>unmodifiable collection</i> is a collection, all of whose
148 * mutator methods (as defined above) are specified to throw
149 * {@code UnsupportedOperationException}. Such a collection thus cannot be
150 * modified by calling any methods on it. For a collection to be properly
151 * unmodifiable, any view collections derived from it *must *also be
unmodifiable.
152 * For example, if a List is unmodifiable, the List returned by
153 * {@link List#subList List.subList} *should *also be unmodifiable.
That leaves room for a non-compliant collection which could not technically be
called "unmodifiable".
I agree that "should" is poor here; I'll reword this to say that the returned
list "is also unmodifiable."
138 * does not support the operation. Such methods *should *(but are not
required
139 * to) throw an {@code UnsupportedOperationException} if the invocation would
140 * have no effect on the collection. For example, invoking the
141 * {@link #addAll addAll} method on a collection that does not support
142 * the {@link #add add} operation *should *throw the exception if
143 * the collection passed as an argument is empty.
These two sentences both allow not throwing UOE and requiring UOE. Can they be
worded to be consistent (or similarly qualified.)
For this case, implementations are recommended to throw UOE, but they are not
required to do so. Some implementations will throw, while others will not throw.
There are examples of both in the JDK. I'll clarify the example, but I really do
mean "should" here.
Set.java: 706: Would using "unique elements" clarify the contents of the
result?
Saying "Duplicate elements are permitted," may be misleading.
Perhaps "The given Collection may contain duplicate elements"...
I'll clarify this to say that if the given Collection contains duplicate
elements, an arbitrary element of the duplicates is preserved.
Similarly in Collectors.to toUnmodifiableSet:
"Duplicate elements are allowed," can be misleading, especially the word
allowed.
Will update similarly.
Collectors.toUnmodifiableMap
* If the mapped keys
1474 * might have duplicates, use {@link #toUnmodifiableMap(Function,
Function, BinaryOperator)}
1475 * instead.
It would helpful to say why to use the version with the BinaryOperator, for
example to say"
"To determine which of the duplicate elements to retain". or similar.
Will add words about handling the merging of values.
Collectors:1606: impl note: With three different NPE throws, it is helpful to
use the 2-arg
form of requireNonNull to indicate which parameter offends.
Will update.
Thanks,
s'marks
Roger
On 10/30/2017 6:50 PM, Stuart Marks wrote:
(also includes 8184690: add Collectors for collecting into unmodifiable List,
Set, and Map)
Hi all,
Here's an updated webrev for this changeset; the previous review thread is here:
http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-September/049261.html
This webrev includes the following:
* specification revisions to provide clearer definitions of "view"
collections, "unmodifiable" collections, and "unmodifiable views"
* new List.copyOf(), Set.copyOf(), and Map.copyOf() "copy factory" methods
* new Collectors.toUnmodifiableList, Set, and Map methods
* tests for the new API methods
I've added some assertions that require some independence between the source
collection (or map) and the result of the copyOf() method.
I've made a small but significant change to Set.copyOf compared to the
previous round. Previously, it specified that the first of any equal elements
was preserved. Now, it is explicitly unspecified which of any equals elements
is preserved. This is consistent with Set.addAll, Collectors.toSet, and the
newly added Collectors.toUnmodifiableSet, none of which specify which of
duplicate elements is preserved.
(The outlier here is Stream.distinct, which specifies that the first element
of any duplicates is preserved, if the stream is ordered.)
I've also made some minor wording/editorial changes in response to suggestions
from David Holmes and Roger Riggs. I've kept the wording changes that give
emphasis to "unmodifiable" over "immutable." The term "immutable" is
inextricably intertwined with "persistent" when it comes to data structures,
and I believe we'll be explaining this forever if Java's "immutable" means
something different from everybody else's.
Webrev:
http://cr.openjdk.java.net/~smarks/reviews/8177290/webrev.1/
Bugs:
https://bugs.openjdk.java.net/browse/JDK-8177290
add copy factory methods for unmodifiable List, Set, Map
https://bugs.openjdk.java.net/browse/JDK-8184690
add Collectors for collecting into unmodifiable List, Set, and Map
Thanks,
s'marks
