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From "Sebb (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LANG-816) introduce ConstantUtils class to prevent Javac from inlining constants
Date Thu, 23 Aug 2012 02:32:42 GMT

    [ https://issues.apache.org/jira/browse/LANG-816?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13440012#comment-13440012
] 

Sebb commented on LANG-816:
---------------------------

I like this idea.

JMeter had the same problem with its Version class which contains constants for the version
and SVN revision.
The solution we adopted was to make the constants private and add getters for the constants.

I suspect the CONST solution may be marginally more efficient as the method is only evaluated
once when the class is instantiated. [In the case of the JMeter getter, the JVM will probably
inline the method.]
                
> introduce ConstantUtils class to prevent Javac from inlining constants
> ----------------------------------------------------------------------
>
>                 Key: LANG-816
>                 URL: https://issues.apache.org/jira/browse/LANG-816
>             Project: Commons Lang
>          Issue Type: Wish
>            Reporter: Julius Davies
>            Priority: Trivial
>
> ConstantUtils could contain a set of methods to ensure constants are not inlined by javac.
>   
> For example, typically a developer might declare a constant like
> {code}
>   public final static int MAGIC_NUMBER = 5;
> {code}
> Should a different jar file refer to this, and the MAGIC_NUMBER is changed a later date
(e.g., MAGIC_NUMBER = 6), the different jar file will need to be recompiled.  This is because
javac typically inlines the primitive or String constant directly into the bytecode, and removes
the reference to the MAGIC_NUMBER field.
> To help the other jar (so that it does not need to recompile when constants are changed)
the original developer can declare their constant using one of the CONST() utility methods,
instead:
> {code}
>   public final static int MAGIC_NUMBER = CONST(5);
> {code}
> I imagine the code would look something like this:
> {code}
> public static boolean CONST(boolean v) { return v; }
> public static byte CONST(byte v) { return v; }
> public static char CONST(char v) { return v; }
> public static short CONST(short v) { return v; }
> public static int CONST(int v) { return v; }
> public static long CONST(long v) { return v; }
> public static float CONST(float v) { return v; }
> public static double CONST(double v) { return v; }
> public static <T> T CONST(T t) { return t; }
> {code}

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