I’m working in a Java project and I’ve started recently to add nullable annotations to method arguments and return values. I was wondering if there are any annotations that can be added to an argument so that it covers generic types as well. Right now I have cases similar to:
Map<String, String> someMethod(Map<String, Map<String, String>> arg) {
...
}
That become:
@NotNull
Map<@NotNull String, @NotNull String> someMethod(@NotNull Map<@NotNull String, @NotNull Map<@NotNull String, @NotNullString>> arg) {
...
}
Which becomes, obviously, hard to read. I’m not very familiar with the internals of Java annotations, so maybe this isn’t possible?
Reducing the number of null annotations can be achieved with a suitable default annotation.
The following applies to annotations from org.eclipse.jdt.annotation_2.x:
In particular @org.eclipse.jdt.annotation.NonNullByDefault is able to influence types in various positions, including type arguments.
So if you write:
@NonNullByDefault
Map<String, String> someMethod(Map<String,Map<String,String>> arg) { ...
this will indeed be interpreted as
@NonNull Map<@NonNull String, @NonNull String> someMethod(@NonNull Map<@NonNull String, @NonNull Map<@NonNull String, @NonNull String>> arg) {
It is even possibly to fine-tune the effect of @NonNullByDefault, and it can be applied to individual methods, or entire classes, packages or modules.
If a signature still contains a few nullable types, those need to be annotated individually as @Nullable in order to override the default, but those exceptions should be much fewer than the nonnull types. Note, that both @NonNull and @Nullable can be attached to types in all relevant positions, again including type arguments.
General documentation on how Eclipse interprets generics-aware null annotations can be found in the online help.