javax.annotation: @Nullable vs @CheckForNull
In the IntelliJ Idea @javax.annotation.Nullable
is supported by default and any attempts to dereference @Nullable
arguments or return values will result in warning.
@alexander-pavlov, You could add @javax.annotation.CheckForNull
in configuration of "Constant conditions & exceptions" inspection. Go File->Settings->Inspections->Probable bugs->Constant conditions & exceptions->Configure annotations.
I prefer doing this as @CheckForNull
has more clear meaning than @Nullable
as @lbalazscs mentioned in his answer above.
I think it is pretty clear from the link you added: if you use @CheckForNull
and the code that uses the value does not check for null
, FindBugs will show it as an error.
FindBugs will ignore @Nullable
.
In practice this annotation is useful only for overriding an overarching
NonNull
annotation.
Use @CheckForNull
in the cases when the value must always be checked. Use @Nullable
where null
might be OK.
EDIT: it seems that @CheckForNull
is not well supported at the moment, so I suggest avoiding it and using @NonNull
(also see Which @NotNull Java annotation should I use?).
Another idea would be to get in touch directly with the FindBugs developers, and ask their opinion about the inconsistency in the documentation.
@Nonnull
and @Nullable
are correctly handled by IntelliJ IDEA. FindBugs found the problem with @Nonnull
but missed those for @Nullable
and @CheckForNUll
. Problems which were detected by IDEA and FindBugs are marked with comments.
package com.db.icestation;
import javax.annotation.CheckForNull;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
public class test {
@Nullable public String nullable() {
return "";
}
@Nonnull public String nonnull() {
return null; // IDEA, findbugs
}
@CheckForNull public String checkForNull() {
return null;
}
public static void main(String[] args) {
System.out.println(new test().nullable().length()); // IDEA
System.out.println(new test().nonnull().length());
System.out.println(new test().checkForNull().length());
}
}