Question

In c\c++ can define:

#ifndef <token>
    /* code */
#else
    /* code to include if the token is defined */
#endif

my question, is there a way to do it in java? (which is not defining a global static variable..)
for example i want to run some code only in debug mode..

thanks!

Answer 1

The answer is No. Not in the sense that you mean.

The way you do this kind of thing in Java as follows:

private static final boolean flag = true;  /* or false :-) */

if (flag) {
   /* code */
} else {
   /* different code */
}

Java doesn’t have a preprocessor (like C and C++ do). However, the compiler will optimize away the unused branch of an if statement like the above, PROVIDED that flag is a compile-time constant expression. This is a limited form of conditional compilation. Note that the controlling flag constant can be imported from a different class.

(IIRC, this behaviour is specified in the JLS … which means that you can rely on any conforming Java compiler to do it.)

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@Treebranch comments that “this” can cause code bloat.

1. If @Treebranch is talking about object code bloat, this is not true. If you do this right with flags/expressions that are compile-time constant expressions as defined by the JLS, then the compiler does not emit any bytecodes for the “conditionally excluded” source code. See @edalorso’s answer.

2. If @Treebranch is are talking about source-code bloat, I agree. But you can say the same thing for #ifdef conditional compilation. (Macros and #include can be used to reduce source-code bloat … but only at the cost of readability, maintainability, etc. And that was the reason that the Java designers refused to support any source-code preprocessing.)

3. Java has a better way of dealing with platform differences, functionality variations and so on: use dynamic binding. If having lots of different plugin classes in your JAR is a concern (bytecode bloat), deal with it by creating a different JAR file for each platform, or whatever.