Annotations

HadjshellLess than 1 minuteNoteLanguageJava

Annotations provide information (metadata) that you need to fully describe your program to the compiler and JVM, but that cannot be expressed in Java
Java 5 feature
In fact, annotation is a special interface which extends Annotation interface
Built-in annotations
- Annotates the code (class, method, variable)
  - @Override
  - @Deprecated
    - Methods can still be used
  - @SuppressWarnings()
    - To turn off inappropriate compiler warnings
  - @SafeVarargs
    - Useful for variable arguments
    - Method must be private or final
  - @FunctionalInterface
    - Describe an interface that has only one method
- Annotates the annotation
  - @Retention(RetentionPolicy.CLASS)
    - Indicates how long annotations with the annotated type are to be retained
  - @Documented
    - Provides support to JavaDoc
  - @Target
    - Indicates the target of the annotation
  - @Inherited
    - Indicates the annocation can be used on subclasses
  - @Repeatable
    - Indicates the annotation can be used multiple times

User-defined annotations

@interface MyAnno {
  String name();
  String date();
  String version() default "1.0";
}

@MyAnno(name="David", date="01/01/1970")
public MyClass {}