enum value used in annotation where a string is expected

Question

Suppose that I have a simple annotation:

 @MyAnnotation(value=<SomeString>)

and an enum:

 enum Days {
      MONDAY...
 }

I cant use this annotation like this:

 @MyAnnotation(value=Days.MONDAY.name())
 private class SomeClass {
       //some code
 }

This code will fail saying that "it must be a compiled time constant". I do understand why this happens and I am aware of the JSL part about compiled time constants.

My question is why and what is the reasoning behind not making an enum a compiled time constant according to the specification. It's not like you can change that enum name...

EDIT for Kumar

private static final class Test {

    public static final String complete = "start" + "finish";

}

The compiler cannot simply execute the name() method to know the value — Kumar Abhinav, Aug 11 '14 at 22:24
What is your edit intending to show? `complete` is not a compile-time constant and as such cannot be used with annotation values. — Luke Woodward, Aug 12 '14 at 07:27
@LukeWoodward you're right, wrong copy paste, my bad. I'm trying to show that you can still perform some computation — Eugene, Aug 12 '14 at 08:04
@Eugene The above String variable "complete" is indeed compile time constant but You can use the variable value directly as compile time constant but not through a funtion even if it is a final method.In the above example,if I define a final method which returns the value of complete variable,then that method cannot act as a compile time constant.For enums,you would need to access the name variable directly and not name() method.I hope I am clear — Kumar Abhinav, Aug 12 '14 at 12:17
@KumarAbhinav I understand that and I know that it works like that - *no problem here*. What I do want to know is why there wasn't a part in the specification about enums in compile time constants. — Eugene, Aug 12 '14 at 12:54
@Eugene Not just enums,it will not work for Strings also if you try to access a final String through a method — Kumar Abhinav, Aug 12 '14 at 13:10
@KumarAbhinav yup, but enums are the obvious choice, cause they can't change. It probably has to do with the fact that the JVM compiles an enum to a class and method dispatching can't be computed to a compile time constant... — Eugene, Aug 12 '14 at 13:11
@Eugene "Method dispatching can't be computed to a compile time constant"..true — Kumar Abhinav, Aug 12 '14 at 13:14
@KumarAbhinav: it wasn't when I wrote that comment. See the edit history. — Luke Woodward, Aug 12 '14 at 15:42
possible duplicate of [Compile time constants and variables](http://stackoverflow.com/questions/9082971/compile-time-constants-and-variables) — Kumar Abhinav, Aug 12 '14 at 17:41
possible duplicate of [How to supply Enum value to an annotation from a Constant in Java](http://stackoverflow.com/questions/13253624/how-to-supply-enum-value-to-an-annotation-from-a-constant-in-java) — Martin Schröder, Jul 31 '15 at 12:40

Kumar Abhinav · Accepted Answer · 2014-08-12T13:17:48.157

2

Method dispatching cannot be computed to a compile time constant

For above example,I am giving an example as case in switch statements also require compile time constant

public class Joshua{

    public final String complete = "start" + "finish";


    public void check(String argument) {


        switch(argument)
        {
         case complete: //This compiles properly
        }

        switch(argument)
        {
         case name(): //This doesn't compile
        }
    }

    public final String name(){

        return complete;
    }

}

With final variables you know it is a compile time constant but methods are free to return anything(a final method simply cannot be overriden)

edited Aug 12 '14 at 13:17

answered Aug 11 '14 at 22:22

Kumar Abhinav

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check my edit, it has nothing to do with "some computation". Also read the JLS part about compile time constants. – Eugene Aug 12 '14 at 05:57
I'm accepting and upvoting for your time, but this is, well, not what I expected.. Thx anyways. – Eugene Aug 12 '14 at 13:19
@Eugene I was unable to phrase the sentence"Method dispatching cannot be computed to a compile time constant".So u deserve it – Kumar Abhinav Aug 12 '14 at 13:25
@Eugene I think u shud see this link http://stackoverflow.com/questions/9082971/compile-time-constants-and-variables – Kumar Abhinav Aug 12 '14 at 18:30
@Eugene it is simply a case of it being a fixed constant but not falling under the definiton of "compile time constant" – Kumar Abhinav Aug 12 '14 at 18:57

enum value used in annotation where a string is expected

1 Answers1