How to supply value to an annotation from a Constant java

Question

I am thinking this may not be possible in Java because annotation and its parameters are resolved at compile time  I have an interface as follows   public interface FieldValues      String   FIELD1   new String    value1    value2        and another class as    SomeAnnotation locations     value1    value2    public class MyClass               I mark many classes with the annotation and I would like to know if I can avoid specifying the strings in every annotation I would instead prefer to use   SomeAnnotation locations   FieldValues FIELD1  public class MyClass               However this gives compilation errors like annotation value should be an array initializer etc  Does someone know how I can use a String constant or String   constant to supply value to an annotation

User · Accepted Answer

Compile constants can only be primitives and Strings:

15.28. Constant Expressions

A compile-time constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly and is composed using only the following:

Literals of primitive type and literals of type String

Casts to primitive types and casts to type String

[...] operators [...]

Parenthesized expressions whose contained expression is a constant expression.

Simple names that refer to constant variables.

Qualified names of the form TypeName . Identifier that refer to constant variables.

Actually in java there is no way to protect items in an array. At runtime someone can always do FieldValues.FIELD1[0]="value3", therefore the array cannot be really constant if we look deeper.

User · Answer

Does someone know how I can use a   String constant or String   constant   to supply value to an annotation    Unfortunately  you can t do this with arrays   With non-array variables  the value must be final static

User · Answer

You re not supplying it with an array in your example  The following compiles fine   public  interface SampleAnnotation       String   sampleValues       public class Values       public static final String val0    A       public static final String val1    B         SampleAnnotation sampleValues   val0  val1        public void foo

User · Answer

You can use a constant  i e  a static  final variable  as the parameter for an annotation   As a quick example  I use something like this fairly often   import org junit Test  import static org junit Assert     public class MyTestClass       private static final int TEST TIMEOUT   60000     one minute per test       Test timeout TEST TIMEOUT      public void testJDK                 assertTrue  Something is very wrong   Boolean TRUE             Note that it s possible to pass the TEST TIMEOUT constant straight into the annotation   Offhand  I don t recall ever having tried this with an array  so you may be running into some issues with slight differences in how arrays are represented as annotation parameters compared to Java variables   But as for the other part of your question  you could definitely use a constant String without any problems   EDIT  I ve just tried this with a String array  and didn t run into the problem you mentioned - however the compiler did tell me that the  attribute value must be constant  despite the array being defined as public static final String     Perhaps it doesn t like the fact that arrays are mutable   Hmm

User · Answer

I am thinking this may not be possible in Java because annotation and its parameters are resolved at compile time     With Seam 2 http   seamframework org  you were able to resolve annotation parameters at runtime  with expression language inside double quotes    In Seam 3 http   seamframework org Seam3 Solder  this feature is the module Seam Solder

User · Answer

You can use enum and refer that enum in annotation field

[java] How to supply value to an annotation from a Constant java

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