Java Annotations @interface (Getting started)

Annotations (also known as metadata) provide a formalized way for us to add information to our code so that we can use it very conveniently at a later point in time.

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1. Define Annotations:

[Java]View PlainCopy 

2. Package com.test;
6. Import Java.lang.annotation.ElementType;
8. Import java.lang.annotation.Retention;
10. Import Java.lang.annotation.RetentionPolicy;
12. Import Java.lang.annotation.Target;
16. @Target (Elementtype.method)
18. @Retention (Retentionpolicy.runtime)
20. Public @interface UseCase {
22. public int id ();
24. Public String Description () default "no description";
26. }

2. In the following class, there are three methods that are annotated as use cases:

[Java]View PlainCopy 

2. Package com.test;
6. Import java.util.List;
10. Public class Passwordutils {
12. @UseCase (id = Description = "Passwords must contain at lease one numeric")
14. Public boolean ValidatePassword (String password) {
16. return password.matches ("\\w*\\d\\w*");
18. }
22. @UseCase (id = )
24. Public string Encryptpassword (string password) {
26. return new StringBuilder (password). reverse (). toString ();
28. }
32. @UseCase (id = $ , description = "New password can ' t equal previously used ones")
34. Public Boolean Checkfornewpassword (list<string> prevpasswords, String password) {
36. return!prevpasswords.contains (password);
38. }
40. }

3. Write the Annotation processor:
[Java]View PlainCopy  

2. Package com.test;
6. Import java.lang.reflect.*;
8. Import java.util.*;
12. Public class Usecasetracker {
14. public static void trackusecases (list<integer> usecases, class<?> cl) {
16. For (Method m:cl.getdeclaredmethods ()) {
18. UseCase UC = M.getannotation (usecase.   Class);
20. if (UC! = null) {
22. System.out.println ("Found use case:" + uc.id () + "" + uc.description ());
24. Usecases.remove (New Integer (Uc.id ()));
26. }
28. }
30. For (int i:usecases) {
32. System.out.println ("warning:missing use case-" + i);
34. }
36. }
40. public static void Main (string[] args) {
42. list<integer> usecases = new arraylist<integer> ();
44. Collections.addall (usecases, 50);
46. Trackusecases (Usecases, passwordutils.   Class);
48. }
50. }

Output:

Found use case:49 New password can ' t equal previously used ones
Found use case:47 passwords must contain at lease one numeric
Found Use case:48 No description
Warning:missing Use case-50

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Java Annotations @interface (Getting started) (GO)