Conditional Java compilation

Question

I'm a longtime C++ programmer, new to Java. I'm developing a Java Blackberry project in Eclipse. Question - is there a way to introduce different configuration sets within the project and then compile slightly different code based on those?

In Visual Studio, we have project configurations and #ifdef; I know there's no #ifdef in Java, but maybe something on file level?

Answer 1

You can set up 'final' fields and ifs to get the compiler to optimize the compiled byte-codes.

...
public static final boolean myFinalVar=false;
...
if (myFinalVar) { 
 do something ....
 ....
}

If 'myFinalVar' is false when the code is compiled the 'do something....' bit will be missed out of the compiled class. If you have more than one condition - this can be tidied up a bit: shift them all to another class (say 'Config.myFinalVar') and then the conditions can all be kept in one neat place.

This mechanism is described in 'Hardcore Java'.

[Actually I think this is the same mechanism as the "poor man's ifdef" posted earlier.]

Answer 2

you can manage different classpath, for example, implement each 'Action' in a set of distinct directories:

dir1/Main.java
dir2/Action.java
dir3/Action.java

then use a different classpath for each version

javac -sourcepath dir1 -cp dir2 dir1/Main.java

or

javac -sourcepath dir1 -cp dir3 dir1/Main.java