[cleanup] Preallocate memory in CollectionUtils
+ cache the collection sizes for iteration
Bug: 282215580
Test: build + boot + perf record
Change-Id: I1c7b205395e92989d3584554d77ed8140d967651
diff --git a/core/java/com/android/internal/util/CollectionUtils.java b/core/java/com/android/internal/util/CollectionUtils.java
index b87027c..4191936 100644
--- a/core/java/com/android/internal/util/CollectionUtils.java
+++ b/core/java/com/android/internal/util/CollectionUtils.java
@@ -120,8 +120,9 @@
public static @NonNull <I, O> List<O> map(@Nullable List<I> cur,
Function<? super I, ? extends O> f) {
if (isEmpty(cur)) return Collections.emptyList();
- final ArrayList<O> result = new ArrayList<>();
- for (int i = 0; i < cur.size(); i++) {
+ final int size = cur.size();
+ final ArrayList<O> result = new ArrayList<>(size);
+ for (int i = 0; i < size; i++) {
result.add(f.apply(cur.get(i)));
}
return result;
@@ -133,7 +134,7 @@
public static @NonNull <I, O> Set<O> map(@Nullable Set<I> cur,
Function<? super I, ? extends O> f) {
if (isEmpty(cur)) return emptySet();
- ArraySet<O> result = new ArraySet<>();
+ ArraySet<O> result = new ArraySet<>(cur.size());
if (cur instanceof ArraySet) {
ArraySet<I> arraySet = (ArraySet<I>) cur;
int size = arraySet.size();
@@ -163,7 +164,7 @@
Function<? super I, ? extends O> f) {
if (isEmpty(cur)) return Collections.emptyList();
List<O> result = null;
- for (int i = 0; i < cur.size(); i++) {
+ for (int i = 0, size = cur.size(); i < size; i++) {
O transformed = f.apply(cur.get(i));
if (transformed != null) {
result = add(result, transformed);
@@ -239,7 +240,7 @@
public static @NonNull <T> List<T> filter(@Nullable List<?> list, Class<T> c) {
if (isEmpty(list)) return Collections.emptyList();
ArrayList<T> result = null;
- for (int i = 0; i < list.size(); i++) {
+ for (int i = 0, size = list.size(); i < size; i++) {
final Object item = list.get(i);
if (c.isInstance(item)) {
result = ArrayUtils.add(result, (T) item);
@@ -273,7 +274,7 @@
public static @Nullable <T> T find(@Nullable List<T> items,
java.util.function.Predicate<T> predicate) {
if (isEmpty(items)) return null;
- for (int i = 0; i < items.size(); i++) {
+ for (int i = 0, size = items.size(); i < size; i++) {
final T item = items.get(i);
if (predicate.test(item)) return item;
}