java - Using class annotations or static properties -

i’m new java , wondering best practices here.

say have generic class (e.g. car), , inherited classes (honda, subaru) share properties.

public abstract class car {   public static short id; }  public class honda extends car {   public static final short id = 1; }  public class subaru extends car {   public static final short id = 2; } 

doesn’t break dry principle? using annotation then?

@retention(retentionpolicy.runtime) @target(elementtype.type) public @interface id {   public short value(); }  public abstract class car { }  @id(1) public class honda extends car { }  @id(2) public class subaru extends car { } 

it of course bit question of taste. not recommend you. annotations metainformation mark fields, methods , classes. id (or nbseats) rather field annotation.

i prefer in case:

public abstract class car {   protected static short id;    public static short getid() {       return id;   } }  class honda extends car {     static {          id = 1;     } }  class subaru extends car {     static {          id = 2;     } } 

edit: sorry: solution flawed :-( car, honda , subaru share same field. have on that:

public static void main(string[] args) {         new honda();         new subaru();         system.out.println(honda.getid());         system.out.println(subaru.getid()); } 

results in

2 2 

i think solution might better:

public abstract class car {     protected abstract short id();      public static short getidof(class<? extends car> carclass)             throws instantiationexception, illegalaccessexception {         return carclass.newinstance().id();     }      public static void main(string[] args) throws instantiationexception,             illegalaccessexception {         system.out.println(car.getidof(honda.class));         system.out.println(car.getidof(subaru.class));     } }  class honda extends car {     protected short id() {         return 1;     } }  class subaru extends car {     protected short id() {         return 2;     } } 

it has advantages:

• it enforces every concrete subclass of car have id (by implementing id()).
• it hides sublasses of car super-class car
• the compiler can check subclasses of car passed getidof()
• it enforces classloader load classes (static-initializers executed when class loaded!)
• many others

it has disadvantages:

• it needs java reflection
• the id()-method non-static
• instances needed invoke id()
• it demands default public constructor in subclasses
• you can pass abstract subclasses getidof()
• many others

keep in mind types of parameters of annotations limited primitive types, string, class, annotation, enumeration , 1-dimensional arrays!