Java annotations are pieces of metadata that provide information about the code they are used with, and can instruct the IDE how to process this code.
In Java, there is a set of built-in annotations. On top of that, IntelliJ IDEA provides a collection of annotations that are available as a separate project. You can add them to the classpath and use in your code.
Add org.jetbrains.annotations to Gradle or Maven projects
To add the library with annotations to a Gradle project, add the
compile 'org.jetbrains:annotations:16.0.2' dependency to the build.gradle file.
For Maven projects, add the
org.jetbrains:annotations:16.0.2 dependency to pom.xml.
Add org.jetbrains.annotations to other projects
Open the Project Structure dialog Ctrl+Shift+Alt+S and select Libraries.
Click , and select From Maven.
In the search field, type
org.jetbrains:annotations:16.0.2if you use JDK 1.8 or later.
For JDK 1.5, 1.6 or 1.7, type
Add org.jetbrains.annotations in the editor
You can also enable annotations using an intention action.
In the editor, type an annotation, for example,
@NotNulland press Alt+Enter:
From the list, select Add 'annotations' to classpath.
The IDE will prompt you to download the library with annotations from Maven.
@Nlsannotation indicates that an annotated code element is a string that needs to be localized.
@NonNlsannotation indicates that an annotated code element is a string which is not visible to users, it doesn't require localization, and it doesn't contain strings requiring localization. When you annotate an element with
@NonNls, localization tools will skip this element and strings inside it.
@PropertyKeyannotation indicates that a method parameter accepts arguments that must be valid property keys in a specific resource bundle. When a string literal that is not a property key in a bundle is passed as a parameter, IntelliJ IDEA highlights it as an error. The annotation is also used to provide completion in string literals passed as parameters.
@TestOnlyannotation indicates that a method or a constructor must be called from testing code only.
The @Contract annotation lets you specify a set of rules (a contract) that a method must follow. If the contract is violated, IntelliJ IDEA reports a problem.
The @Nullable annotation indicates a variable, parameter, or return value that can be null.
The @NotNull annotation indicates a variable, parameter, or return value that cannot be null.