Annotation

Annotation Types

• May apply to:
  • packages,
  • types,
  • variables,
  • constructors,
  • methods and parameters
  • type case: myString = (@NotNull String) str;
  • implements: class UnModifiableList<T> implements @Readonly List<@Readonly T>
  • throws declaration: void monitorTemperature() throws @Critical TemperatureException {...}
• NOT on object / instance
• Elements
  • optional name / value pairs
  • value can be primitives, strings, enums and arrays of them
  • may define default values for some or all

Annotation types are special interfaces

    public @interface Author {         String name();         String created();         int revision() default 1;         String[] reviewers() default {};     }     public @interface Complexity {         ComplexityLevel value() default ComplexityLevel.MEDIUM;     }     public enum ComplexityLevel {         VERY_SIMPLE, SIMPLE, MEDIUM, COMPLEX, VERY_COMPLEX;     }

    // nested enum 

public @interface Complexity { public enum Level { VERY_SIMPLE, SIMPLE, MEDIUM, COMPLEX, VERY_COMPLEX; }

Annotation that applies to other annotations

• @Retention (RetentionPolicy.SOURCE/CLASS/RUNTIME)
• @Documented (by default annotations are not included in Javadoc)
• @Target(ElementType.ANNOTATION_TYPE/CONSTRUCTOR/FIELD/LOCAL/METHOD/PACKAGE/PARAMETER/TYPE)
• @Inherited: annotation can be inherited from super class (not true by default)
• @Repeatable

Obtain annotation

Type annotation: annotatedObject.getClass().getAnnotation(AnnotationType.class)