Is there something similar to the C/C++ compiler directive #ifdef,
#define, and #endif in Java? I would like to compile
debugging code conditionally.
This is one of the first questions that crossed my mind when I first
started programming in Java. The disappointing answer is no. Not
everyone agrees on the need for Java to include flexible
conditional compilation support or some of the other beneficial
features provided by a preprocessor.
Nonetheless, there are several
rather compelling reasons for using a preprocessor beyond
conditionally compiling debugging code. The most compelling reason
that developers are facing on an increasing basis is the need to
maintain different versions of classes from the same source file. A
prime example of this today is when you need to support a class
library for both Java 2 Standard Edition and Java 2 Micro Edition.
When all you have to do is remove import java.io.* and make a class
not implement java.io.Serializable to make it work for J2ME,
conditional compilation is just the right thing. Even though there
are alternative ways of approaching the problem, they typically result
in code bloat.
For the case of maintaining debugging code, a widely suggested
approach is to declare a static final Boolean constant, initializing
it to True when you want to turn debugging on and to False when you
want it off. Then place debugging code inside an If statement that
tests the value of the constant. This allows the compiler to optimize
out all debugging code when the constant's value is equal to False.
This approach is inadequate for solving the general problem of
conditional compilation, but it will allow you to conditionally
include debugging code.
You may want to search the Web for one of
several preprocessor implementations for Java, but keep in mind that
none of them is standard.