Java Reference
In-Depth Information
Anotherexampleofaninternalinvariantconcernsaswitchstatementwithnodefault
case.Thedefaultcaseisavoidedbecausethedeveloperbelievesthatallpathshavebeen
covered. However, this is not always true, as
Listing 3-34
demonstrates.
Listing 3-34.
Another buggy internal invariant
class IIDemo
{
final static int NORTH = 0;
final static int SOUTH = 1;
final static int EAST = 2;
final static int WEST = 3;
public static void main(String[] args)
{
int direction = (int) (Math.random()
*5
);
switch (direction)
{
case
NORTH:
System.out.println("travelling
north"); break;
case
SOUTH:
System.out.println("travelling
south"); break;
case EAST : System.out.println("travelling east");
break;
case WEST : System.out.println("travelling west");
break;
default
: assert false;
}
}
}
Listing 3-34
assumes that the expression tested by switch will only evaluate to one
offourintegerconstants.However,
(int) (Math.random()*5)
canalsoreturn4,
causingthedefaultcasetoexecute
assert false;
,whichalwaysthrows
Asser-
tionError
. (You might have to run this application a few times to see the assertion
error, but first you need to learn how to enable assertions, which I discuss later in this
chapter.)
