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EnumTypeAdapter constructor optimization #2734

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merged 3 commits into from
Sep 3, 2024
Merged

EnumTypeAdapter constructor optimization #2734

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c6b1964
EnumTypeAdapter constructor optimization
esaulpaugh Sep 3, 2024
83741ec
reuse the fields array
esaulpaugh Sep 3, 2024
bc435b3
add comment about the necessity of unconditionally trimming the field…
esaulpaugh Sep 3, 2024
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15 changes: 9 additions & 6 deletions gson/src/main/java/com/google/gson/internal/bind/EnumTypeAdapter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@
import java.io.IOException;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

Expand Down Expand Up @@ -59,17 +59,20 @@ private EnumTypeAdapter(final Class<T> classOfT) {
// Uses reflection to find enum constants to work around name mismatches for obfuscated
// classes
Field[] fields = classOfT.getDeclaredFields();
ArrayList<Field> constantFieldsList = new ArrayList<>(fields.length);
int constantCount = 0;
for (Field f : fields) {
// Filter out non-constant fields, replacing elements as we go
if (f.isEnumConstant()) {
constantFieldsList.add(f);
fields[constantCount++] = f;
}
}

Field[] constantFields = constantFieldsList.toArray(new Field[0]);
AccessibleObject.setAccessible(constantFields, true);
// Trim the array to the new length
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My initial thought was that most of the time you won't need to do this. Every call to getDeclaredFields() returns a new array and if there are no fields that are not enum constants then you can just use that array as is. However, with javac at least, it turns out that there is always a private $VALUES field which is an array that is cloned every time values() is called on the enum. So perhaps add a further note like "This will always be needed because of the $VALUES field."

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@esaulpaugh esaulpaugh Sep 3, 2024 •
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Good call; comment added.

Also, the enum constants all seem to appear first among the declared fields, which would allow reusing the unmodified array (up to the first non-enum constant), but the documentation warns not to rely on that behavior. But at least branch prediction should be good.

fields = Arrays.copyOf(fields, constantCount);

for (Field constantField : constantFields) {
AccessibleObject.setAccessible(fields, true);

for (Field constantField : fields) {
@SuppressWarnings("unchecked")
T constant = (T) constantField.get(null);
String name = constant.name();
Expand Down