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8299444: java.util.Set.copyOf allocates needlessly for empty input collections

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Reviewed-by: rriggs, shade, smarks
This commit is contained in:
Viktor Klang 2023-01-26 18:15:56 +00:00 • committed by Stuart Marks
parent d98a323a8b
commit a2a7703370
3 changed files with 10 additions and 4 deletions
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8
src/java.base/share/classes/java/util/ImmutableCollections.java
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2016, 2021, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2016, 2023, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -166,10 +166,12 @@ class ImmutableCollections {
*/
@SuppressWarnings("unchecked")
static <E> List<E> listCopy(Collection<? extends E> coll) {
if (coll instanceof List12 || (coll instanceof ListN && ! ((ListN<?>)coll).allowNulls)) {
if (coll instanceof List12 || (coll instanceof ListN<?> c && !c.allowNulls)) {
return (List<E>)coll;
} else if (coll.isEmpty()) { // implicit nullcheck of coll
return List.of();
} else {
return (List<E>)List.of(coll.toArray()); // implicit nullcheck of coll
return (List<E>)List.of(coll.toArray());
}
}