My project requires Java 1.6 for compilation and running. Now I have a requirement to make it working with Java 1.5 (from the marketing side). I want to replace method body (return type and arguments remain the same) to make it compiling with Java 1.5 without errors.
Details: I have an utility class called OS
which encapsulates all OS-specific things. It has a method
public static void openFile(java.io.File file) throws java.io.IOException { // open the file using java.awt.Desktop ... }
to open files like with double-click (start
Windows command or open
Mac OS X command equivalent). Since it cannot be compiled with Java 1.5, I want to exclude it during compilation and replace by another method which calls run32dll
for Windows or open
for Mac OS X using Runtime.exec
.
Question: How can I do that? Can annotations help here?
Note: I use ant, and I can make two java files OS4J5.java
and OS4J6.java
which will contain the OS
class with the desired code for Java 1.5 and 1.6 and copy one of them to OS.java
before compiling (or an ugly way – replace the content of OS.java
conditionally depending on java version) but I don’t want to do that, if there is another way.
Elaborating more: in C I could use ifdef, ifndef
, in Python there is no compilation and I could check a feature using hasattr
or something else, in Common Lisp I could use #+feature
. Is there something similar for Java?
Found this post but it doesn’t seem to be helpful.
Any help is greatly appreciated. kh.
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Answer
Nope there isn’t any support for conditional compilation in Java.
The usual plan is to hide the OS specific bits of your app behind an Interface
and then detect the OS type at runtime and load the implementation using Class.forName(String)
.
In your case there no reason why you can’t compile the both OS*
(and infact your whole app) using Java 1.6 with -source 1.5 -target 1.5
then in a the factory method for getting hold of OS
classes (which would now be an interface) detect that java.awt.Desktop
class is available and load the correct version.
Something like:
public interface OS { void openFile(java.io.File file) throws java.io.IOException; } public class OSFactory { public static OS create(){ try{ Class.forName("java.awt.Desktop"); return new OSJ6(); }catch(Exception e){ //fall back return new OSJ5(); } } }