Constant expression required

Question

(Original thread http://forum.java.sun.com/thread.jsp?forum=31&thread=428634)
Hello all,
in the following class, if the comment is removed, the compiler complains that a constant expression is required.
class Test {
final static int A;
final static int B=5;
static {
A=5;
public static void main(String args[]) {
switch(1) {
//case A:
case B:
Is this a bug? Is this a feature? How could A not be a constant expression?
Is it good coding style to initialize constant variables at declaration time and not in the static block?
7Kami

Answer 1

(Original thread
http://forum.java.sun.com/thread.jsp?forum=31&thread=42
634)
Hello all,
in the following class, if the comment is removed, the
compiler complains that a constant expression is
required.
class Test {
final static int A;
final static int B=5;
static {
A=5;
public static void main(String args[]) {
switch(1) {
//case A:
case B:
Is this a bug? Is this a feature? How could A not be a
constant expression?JLS goes to a lot of detail explaining why this is a language feature. It is required to support Java's requirement to never have unreachable code. In order to do that, the compiler need to have compile-time const expressions in case labels (otherwise it can never detect at static compilation time whether a case branch is reachable or not [e.g., because it clashes with another case label]). Those expressions could be either literals or static finals etc.
This, BTW, explains why inlining of static finals is not just an optimization but an essential language requirement.
The relevant JLS sections to read are 14.20 and 13.4.8.