如何在包上使用NonNullByDefault

Question

My compiler warns me about A default nullness annotation has not been specified for the package . I'm using Juno with Java 7.

The documentation stats you should add @NonNullByDefault as a package option, but I don't know what that means.

Can I somehow set NonNullByDefault for the whole package? In Eclipse I can't right click on a package and say add option or something similar.

Or do I just add @NonNullByDefault to any class in a package and then it's valid for all beans in that package? Or do I have to create some meta info file in the pakage to add package options? I must be blind because I can't find any help online....

A small example would be great.

Answer 1

Summary:
Getting the above advice to work was not intuitive to me. Nor was the actual solution I just figured out. In the package-info.java file:
a. put the annotation ABOVE the package declaration
b. put the NonNullByDefault annotation import AFTER the package declaration

---

Details:
I don't know if I am the only person who read the above answers and couldn't figure out how to get this working. So, just to be extra clear, here's the (non-obvious nor intuitive) steps I took to get this to finally work in Eclipse-Juno:

1. In Package Explorer, goto the root Java package showing the warning (or error) message starting with " A default nullness annotation has not been specified for the package... " - for this example, please assume the package name of "org.public_domain"
2. On the Java package, activate the right-click-menu and select the " New -> Package " option - yes, I know your package already exists, consider it an eclipse idiosyncrasy - it's not going to do anything to your existing package
3. When the " New Java Package " dialog appears, check the " Create package-info.java " checkbox and click "Finish"

4. Your Java editor will now have a new file titled " package-info.java " displayed with the following content:

    /** * */ /** * @author xyz * */ package org.public_domain; 

5. Now, rearrange the file content to look like this:

    /** * */ /** * @author xyz * */ @NonNullByDefault package org.public_domain; import org.eclipse.jdt.annotation.NonNullByDefault; 

   ...or like this...

    /** * */ /** * @author xyz * */ @org.eclipse.jdt.annotation.NonNullByDefault package org.public_domain; 

6. Enjoy the awesomeness that is eclipse @NonNullByDefault

My challenge was figuring out that I was to put the annotation ABOVE the package declaration . And to put the NonNullByDefault annotation import AFTER the package declaration . For me, that was not intuitive.

Hope this saves someone else the time I've ended burning up chasing down this particular pathway.

Answer 2

If you simply want to get rid of the warning and ignore this feature because you're not making use of it, you can simply disable it in the Eclipse preferences:

Window > Preferences > Java > Compiler > Errors/Warnings > Null analysis > Missing '@NonNullByDefault' annotation on package = [Ignore]

Answer 3

See the source code or JavaDocs:

Note that for applying an annotation to a package a file by the name
package-info.java is used.

And:

@Target({PACKAGE,TYPE,METHOD,CONSTRUCTOR})