Local caching of Java constants

Question

Let's say I have a Java app which uses a (static) int constant from a library:

int myval = OutsideLibraryClass.CONSTANT_INT;

Now, without recompiling my app, I run it against a slightly different version of OutsideLibraryClass, in which the value of CONSTANT_INT is different.

Is my app going to see the new value (because it picks it up at runtime) or the old (because the value is compiled into the bytecode in my method)? Does it make any difference if CONSTANT_INT is final? Is there a part of the Java spec that talks about this?

Answer 1

References to constant fields are resolved at compile time to the constant values they denote. (JLS 13.1)

Answer 2

Unfortunately your question is not specific enough to answer the question, because it may or may not change without recompiling. Here's an example where the constant value will change with out recompiling.

public class Const {
   public static final int CONSTANT;
   static {
      CONSTANT = 4;
   }
}

class Test
{
   int c = Const.CONSTANT;
}

And here's a case where it will not change without recompiling

public class Const {
   public static final int CONSTANT = 4;
}

class Test
{
   int c = Const.CONSTANT;
}