RFR(m): 8177290 add copy factory methods for unmodifiable List, Set, Map
stuart.marks at oracle.com
Wed Nov 29 05:21:41 UTC 2017
On 11/22/17 8:45 AM, Remi Forax wrote:
> I think i prefer toImmutableList() than toUnmodifiableList() because the List
> is truly immutable and not an unmodifiable proxy in front of a mutable List
> (like Collections.unmodifiableList() does).
Immutability is like wine.
If you put a spoonful of wine in a barrel full of sewage, you get sewage. If you
put a spoonful of sewage in a barrel full of wine, you get sewage.
(Schopenhauer's Law of Entropy)
Similarly, if you add a little immutability to something mutable, you get
mutability. And if you add a little mutability to something immutable, you get
To get the desired properties of immutability (e.g., thread-safety, or the
ability to hand around references safely without making defensive copies), it's
insufficient for a collection to be "immutable"; you also have to make some
statements about the contents. It's thus more precise to say that a collection
is unmodifiable, and to provide a clear definition of an unmodifiable collection.
Although unmodifiable collections have been around since the collections
framework was introduced, oddly enough the concept has never had a good
definition. The current proposal includes definitions for unmodifiability,
unmodifiable collections, and unmodifiable views, and it clearly specifies which
APIs return unmodifiable views and which return unmodifiable collections.
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