As far as I understand the Java 8 JLS the expression (1/0) is considered a constant expression, but when I try to compile the following program with OpenJDK 8 I get an error
public class Switch {
public static void main(String[] args) {
switch(42) {
case (1/0):
return;
default:
return;
}
}
}
The error says (1/0) isn't a constant expression
Switch.java:4: error: constant expression required
case (1/0):
^
1 error
Am I missing something? Or is it a bug in OpenJDK 8?
The compiler is doing constant folding (precomputing trivial literal expressions). This is a case where the expression "completes abruptly", to use the JLS verbiage, disqualifying it from meeting the definition of "constant expression". So it's not a bug, it's consistent with the JLS.
And yes, the expression doesn't evaluate to a value either (warning the user trying to do something like this that the result will not be a constant expression), but the compiler doesn't know that until it tries. Not evaluating to a value and completing abruptly would seem to go hand-in-hand.
Adding a variable declaration like
int x = 1 / 0;
doesn't cause a compiler error, it's the switch that forces the expression to be evaluated at compile time.
By the way I checked that this happens for version 7 of the Oracle and IBM JDKs too, it's not OpenJDK or JDK8 specific.
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