We have a library we've written and after introducing the Checker Framework NullnessChecker to verify its code, it fails to compile (as expected). I've fixed all the obvious errors, but this one I cannot find out how to fix...
Here's the offending function's signature:
private static @Nullable char[] getChars(char ch)
And the call site where the error occurs:
@Nullable char[] replacement = getChars( string.charAt( index ) );
Can anyone tell me how to get checker to accept this? It seems to me to be correct code.
EDIT
The error:
[type.invalid] [@Initialized, @Nullable] may not be applied to the type "@Initialized @Nullable char"
The error message
[@Initialized, @Nullable] may not be applied to the type "@Initialized @Nullable char"
would have been clearer if it had just been
@Nullable may not be applied to the type "char"
The issue is that char is a primitive type. It doesn't make sense to speak of @Nullable char or @NonNull char. Nullness is applicable only to object (non-primitive) types. The same is true of initialization.
If you want to specify a nullable array of char -- that is, the variable replacement is either null or is an array of char -- then write it this way:
char @Nullable [] replacement = ...;
If you write
@Nullable char [] replacement = ...;
then that is an array of @Nullable char.
This is a standard part of the Java type annotation syntax, and is not specific to the Checker Framework. However, there is a FAQ about this in the Checker Framework manual.