processing actually does know the current project directory. you can load and save files without any directory.
you can also go from there to a folder inside your sketch folder, for example loadImage("data/1.jpg"); or a previous folder loadImage(../1.jpg); or do you really need the NAME ?

If you mean the sketch's path, you can access it via the public field sketchPath.     

Yes, i need to know the path in my program!
what do u mean by public field sketchPath?

Use sketchPath() and dataPath() to get a path to your sketch and data folders.

just in case somebody needs it...

println(dataPath(""));

mind the ""

1. println(sketchPath);
2. println(sketchPath("Foo.txt"));
3. println(dataPath("Bar.txt"));
4. File sp = sketchFile("Foo.txt");
5. File dp = dataFile("Bar.txt");
6. println(sp.getAbsolutePath());
7. println(dp.getAbsolutePath());