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8156079: consider making empty instances singletons

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8169222: minor immutable collections optimizations

Reviewed-by: forax, redestad, alanb
This commit is contained in:
Stuart Marks 2016-11-04 14:29:34 -07:00
parent 766e807c18
commit d55905fe1b
4 changed files with 36 additions and 14 deletions
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38
jdk/src/java.base/share/classes/java/util/ImmutableCollections.java
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@ -53,7 +53,8 @@ class ImmutableCollections {
*/
static final int SALT;
static {
SALT = new Random().nextInt();
long nt = System.nanoTime();
SALT = (int)((nt >>> 32) ^ nt);
}
/** No instances. */
@ -63,7 +64,7 @@ class ImmutableCollections {
* The reciprocal of load factor. Given a number of elements
* to store, multiply by this factor to get the table size.
*/
static final double EXPAND_FACTOR = 2.0;
static final int EXPAND_FACTOR = 2;
static UnsupportedOperationException uoe() { return new UnsupportedOperationException(); }
@ -84,7 +85,14 @@ class ImmutableCollections {
}
static final class List0<E> extends AbstractImmutableList<E> {
List0() { }
private static final List0<?> INSTANCE = new List0<>();
@SuppressWarnings("unchecked")
static <T> List0<T> instance() {
return (List0<T>) INSTANCE;
}
private List0() { }
@Override
public int size() {
@ -214,7 +222,14 @@ class ImmutableCollections {
}
static final class Set0<E> extends AbstractImmutableSet<E> {
Set0() { }
private static final Set0<?> INSTANCE = new Set0<>();
@SuppressWarnings("unchecked")
static <T> Set0<T> instance() {
return (Set0<T>) INSTANCE;
}
private Set0() { }
@Override
public int size() {
@ -351,7 +366,7 @@ class ImmutableCollections {
SetN(E... input) {
size = input.length; // implicit nullcheck of input
elements = (E[])new Object[(int)Math.ceil(EXPAND_FACTOR * input.length)];
elements = (E[])new Object[EXPAND_FACTOR * input.length];
for (int i = 0; i < input.length; i++) {
E e = Objects.requireNonNull(input[i]);
int idx = probe(e);
@ -450,7 +465,14 @@ class ImmutableCollections {
}
static final class Map0<K,V> extends AbstractImmutableMap<K,V> {
Map0() { }
private static final Map0<?,?> INSTANCE = new Map0<>();
@SuppressWarnings("unchecked")
static <K,V> Map0<K,V> instance() {
return (Map0<K,V>) INSTANCE;
}
private Map0() { }
@Override
public Set<Map.Entry<K,V>> entrySet() {
@ -529,7 +551,7 @@ class ImmutableCollections {
}
size = input.length >> 1;
int len = (int)Math.ceil(EXPAND_FACTOR * input.length);
int len = EXPAND_FACTOR * input.length;
len = (len + 1) & ~1; // ensure table is even length
table = new Object[len];
@ -789,7 +811,7 @@ final class CollSer implements Serializable {
return Set.of(array);
case IMM_MAP:
if (array.length == 0) {
return new ImmutableCollections.Map0<>();
return ImmutableCollections.Map0.instance();
} else if (array.length == 2) {
return new ImmutableCollections.Map1<>(array[0], array[1]);
} else {