tilgalas commented on code in PR #32081:
URL: https://github.com/apache/beam/pull/32081#discussion_r1816634987
##########
sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/FieldValueGetter.java:
##########
@@ -29,7 +30,7 @@
* <p>Implementations of this interface are generated at runtime to map object
fields to Row fields.
*/
@Internal
-public interface FieldValueGetter<ObjectT, ValueT> extends Serializable {
+public interface FieldValueGetter<ObjectT extends @NonNull Object, ValueT>
extends Serializable {
Review Comment:
so apparently there's a difference (I don't understand why it would be so,
though) between a `@NonNull T` and `T extends @NonNull Object` - here's an
example, consider:
```
public interface I<T extends @NonNull Object> {
T getT();
}
```
with a signature as above, we can only write:
```
public static <T extends @NonNull Object> void f(I<T> i) {
System.out.println(i.getT().getClass());
}
```
or alternatively:
```
public static <T> void f(I<@NonNull T> i) {
System.out.println(i.getT().getClass());
}
```
The checkerframework will make sure that we propagate the non-nullness of
the parameter.
This won't work for example:
```
public static <@Nullable T> void f(I<T> i) {
T t = i.getT();
if (t != null) {
System.out.println(t.getClass());
}
}
```
nor will this:
```
public static <T> void f(I<@Nullable T> i) {
T t = i.getT();
if (t != null) {
System.out.println(t.getClass());
}
}
```
but it will work if I change the signature of `I` to:
```
public interface I<@NonNull T> {
T getT();
}
```
in other words, the `@NonNull T` annotation on the interface is not really
enforced anywhere, it's more like a suggestion, and so it's not really
expressing the concept of the interface only works with `@NonNull` types
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