Avoid allocations in FieldSet.mergeFromField
- Pre-size ArrayList
- Avoid iterator allocation
PiperOrigin-RevId: 653905397
diff --git a/java/core/src/main/java/com/google/protobuf/FieldSet.java b/java/core/src/main/java/com/google/protobuf/FieldSet.java
index 9ddf548..debad4e 100644
--- a/java/core/src/main/java/com/google/protobuf/FieldSet.java
+++ b/java/core/src/main/java/com/google/protobuf/FieldSet.java
@@ -517,7 +517,8 @@
}
}
- @SuppressWarnings({"unchecked", "rawtypes"})
+ // Avoid iterator allocation.
+ @SuppressWarnings({"unchecked", "ForeachList", "ForeachListWithUserVar"})
private void mergeFromField(final Map.Entry<T, Object> entry) {
final T descriptor = entry.getKey();
Object otherValue = entry.getValue();
@@ -528,11 +529,16 @@
throw new IllegalStateException("Lazy fields can not be repeated");
}
Object value = getField(descriptor);
+ List<?> otherList = (List<?>) otherValue;
+ int otherListSize = otherList.size();
if (value == null) {
- value = new ArrayList<>();
+ value = new ArrayList<>(otherListSize);
}
- for (Object element : (List) otherValue) {
- ((List) value).add(cloneIfMutable(element));
+ List<Object> list = (List<Object>) value;
+ // Avoid iterator allocation.
+ for (int i = 0; i < otherListSize; i++) {
+ Object element = otherList.get(i);
+ list.add(cloneIfMutable(element));
}
fields.put(descriptor, value);
} else if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE) {
