Getting Started: Compiling,Running, and Debugging - Java - page 40

See Also
Numerous other tools perform extra checking on your Java code. See my book Checking
Java Programs with Open Source Tools (O'Reilly).
Conditional Debugging Without #ifdef
Problem
You want conditional compilation and Java doesn't seem to provide it.
Solution
Use constants, command-line arguments, or assertions (see Maintaining Program Correctness
with Assertions ) , depending upon the goal.
Discussion
Some older languages such as C, PL/I, and C++ provide a feature known as conditional com-
pilation. Conditional compilation means that parts of the program can be included or ex-
cluded at compile time based upon some condition. One thing it's often used for is to include
or exclude debugging print statements. When the program appears to be working, the deve-
loper is struck by a fit of hubris and removes all the error checking. A more common ra-
tionale is that the developer wants to make the finished program smaller—a worthy goal—or
make it run faster by removing conditional statements.
Conditional compilation?
Although Java lacks any explicit conditional compilation, a kind of conditional compilation
is implicit in the language. All Java compilers must do flow analysis to ensure that all paths
to a local variable's usage pass through a statement that assigns it a value first, that all returns
from a function pass out via someplace that provides a return value, and so on. Imagine what
the compiler will do when it finds an if statement whose value is known to be false at com-
pile time. Why should it even generate code for the condition? True, you say, but how can
the results of an if statement be known at compile time? Simple: through final boolean
variables. Further, if the value of the if condition is known to be false, the body of the if