The document discusses annotations and their disadvantages. It provides examples of how annotations are used for different purposes like defining compiler behavior, dependency injection, serialization, validation, defining HTTP methods, aspect-oriented programming, and unit testing. It then provides an example of how annotations can introduce unclear dependencies and lack of encapsulation. It suggests using an object-oriented approach with interfaces instead of a procedural approach with annotations to address these issues.

1. /24@yegor256 1
Аннотации — это зло
Yegor Bugayenko
Annotations Are Evil

2. /24@yegor256 2
“Егор в своем стиле: все
гондурасы, а я д’Артаньян.”
Д’Артаньян и три мушкетёра (1978)

3. /24@yegor256 3
“Попал как будто на выступление
лидера какой-то секты.”
The Evil Cult (1993)

4. /24@yegor256 4
“Автор — маньяк.”
The Silence of the Lambs (1991)

5. /24@yegor256 5
1000+
takes.org
14000+
jcabi.com
rultor.com
jare.io
since
1988
2007
250+

6. /24@yegor256 6
since 2014

7. /24@yegor256 7
Compiler: @Override, @Deprecated, @SuppressWarning
DI: @Inject, @Singleton, etc.
Serialization: @XmlElement, etc.
Validation: @NotNull, etc.
Behavior: @GET, @Transaction
AOP: @RetryOnFailure, @Cacheable
Unit testing: @Test, @Before, @Rule, etc.
Lombok: @ToString, @EqualsAndHashCode, etc.
Something else?…

8. /24@yegor256 8
class Page {
@GET
String index() {
return “Hello, world!”;
}
}

9. /24@yegor256 9
class Page {
String index(Request request) {
if (request.method().equals(“GET”)) {
return “Hello, world!”;
}
return “Method not allowed”;
}
}

10. /24@yegor256 10
class Page {
@GET
String index() {
return “Hello, world!”;
}
}
class Dispatcher {
String dispatch(Page page, Request request) {
if (request.method().equals(“GET”)
&& page.getClass().getMethod(“index”)
.isAnnotationPresent(GET.class)) {
return page.index();
}
return “Method not allowed”;
}
}

11. /24@yegor256 11
Page Dispatcher

12. /24@yegor256 12
Page
Dispatcher
1 upside down

13. /24@yegor256 13
Page
Dispatcher
2 unclear dependencies
???

14. /24@yegor256 14
—Ты BeanPostProcessor видишь?
—Нет.
—А он есть!
ДМБ (2000)

15. /24@yegor256 15
Page
3 no encapsulation
Data

16. /24@yegor256 16
HelloPage
GETPage

17. /24@yegor256 17
class HelloPage implements Page {
@Override
String index(Request request) {
return “200 Hello, world!”;
}
}
class GETPage implements Page {
private final Page page;
@Override
String index(Request request) {
if (request.method().equals(“GET”)) {
return page.index();
}
return “Method not allowed”;
}
}

18. /24@yegor256 18
procedural

19. /24@yegor256 19
object-oriented

20. /24@yegor256 20
Compiler: @Override, @Deprecated, @SuppressWarning
DI: @Inject, @Singleton, etc.
Serialization: @XmlElement, etc.
Validation: @NotNull, etc.
Behavior: @GET, @Transaction
AOP: @RetryOnFailure, @Cacheable
Unit testing: @Test, @Before, @Rule, etc.
Lombok: @ToString, @EqualsAndHashCode, etc.

21. /24@yegor256 21

22. /24@yegor256 22
Can I see the code?Можно ли посмотреть код?

23. /24@yegor256 23
The Shining (1980)

24. /24@yegor256 24
yegor256.com