Java annotations example

• Annotations are metadata (not simple functions as in python) tied the code.
• Annotations are implemented by @interfaces where methods are arguments to the annotation.
  • see https://docs.oracle.com/javase/7/docs/technotes/guides/language/annotations.html
• default defines a default value for a argument in its absence.
• Retation policy defines the metadata life time. It may be
  • Runtime
  • Class (Retained in the .class but not loaded by JVM)
  • Source (Discarted by the compiler)
• Annotations processing depends on the retation:
  • Runtime: Is processed with instrospection at runtime (this example)
  • Source: Is processed by javac -processor
  • Class: ???
• Target determine what kind if entity this annotation annotated, for example:
  • Method
  • Field
  • Class
  • .. etc (see https://docs.oracle.com/javase/7/docs/api/java/lang/annotation/ElementType.html)