Your source code can contain various annotations. For example, @Nullable and @NotNull annotations are used, when IntelliJ IDEA supposes that a certain element can become Null. The @NonNls annotation is used to ignore the hard-coded string literals.
- Make sure that annotations.jar that can be found in the lib folder
under the IntelliJ IDEA installation, is added to the module dependencies.
For @javax.annotation.ParametersAreNonnullByDefault annotations, javax should be added to the module libraries.
You can also use annotations from JSR-305 and FindBugs. In this case, make sure they are added to the classpath.
You can configure @Nullable, @NotNull and @Contract annotations in the Inspections page of the Settings dialog (Constant conditions and exceptions - Configure annotations).
- Introduce the desired annotation before the package/class/field/variable/method/method parameter declaration.