Moving to core-libs-dev ...
On 12/09/2017 5:40 AM, Сергей Цыпанов wrote:
Hi,
looking into the code of java.util.Collections I've found out that
EmptyList#toArray() and EmptySet#toArray() both instantiate new instance of
Object[] at each call. As far as Java array is immutable it's possible to cache
empty Object array and return this cached instance.
There is a slight issue with the specification of toArray here:
"The returned array will be "safe" in that no references to it are
maintained by this list. (In other words, this method must allocate a
new array even if this list is backed by an array). "
Of course for a zero-sized array it is perfectly safe to return a cached
array, but the spec currently requires that a new array be returned.
Cheers,
David
-----
Patch.txt is attached to the body of this mail.
Thanks,
- Sergei Tsypanov
patch.txt
diff --git a/src/java.base/share/classes/java/util/Collections.java
b/src/java.base/share/classes/java/util/Collections.java
--- a/src/java.base/share/classes/java/util/Collections.java
+++ b/src/java.base/share/classes/java/util/Collections.java
@@ -108,6 +108,11 @@
private static final int INDEXOFSUBLIST_THRESHOLD = 35;
/**
+ * Cached empty array
+ */
+ private static final Object[] EMPTY_ARRAY = {};
+
+ /**
* Sorts the specified list into ascending order, according to the
* {@linkplain Comparable natural ordering} of its elements.
* All elements in the list must implement the {@link Comparable}
@@ -4329,7 +4334,7 @@
public boolean contains(Object obj) {return false;}
public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
- public Object[] toArray() { return new Object[0]; }
+ public Object[] toArray() { return EMPTY_ARRAY; }
public <T> T[] toArray(T[] a) {
if (a.length > 0)
@@ -4458,7 +4463,7 @@
public boolean contains(Object obj) {return false;}
public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
- public Object[] toArray() { return new Object[0]; }
+ public Object[] toArray() { return EMPTY_ARRAY; }
public <T> T[] toArray(T[] a) {
if (a.length > 0)
