shell_exec fails to compile java class?

Hello! I need to use shell_exec (or any other similar function) in order to compile a java class-file. I have all the needed components installed on my computer (Windows XP with Java SDK) - I can use "java c:\path...." in order to compile using Start->Run. When I try to do the same with shell_exec or `` it returns null and it doesn't compiles. Even when there are errors - it doesn't show them at all. I've tried to use instead of "java c:\path..." the full java command line compiler path but it didn't work either. When I try functions such as "echo test" it works. Clearly I'm missing here something - problem is... what? -- Use ROT26 for best security