designer?

To Program in C or C++ Use XCode.

For Java, use any text editor, or down load jGrasp http://www.jgrasp.org/

TEG

Do you have any programming experience?

http://www.programmersheaven.com thats a good start. Umm... you can use Fast Light Tool Kit with Mac's, FLTK, which works real well when porting to other systems like Linux, Windows, Unix, etc. (Well mac is unix based). Anyways, I'd use FLTK if you're programming for a multi-platform, but it doesn't have the window scheme like the other systems do. IT has its own grey scheme. For programming macs, just do a search or that. If you want an example code of FLTK (its so simple) just ask and I'll post it. The FLTK source code is so easy to read through and see how to use properties (provided that you've programmed before) you can learn it just by the source. BTW it uses C/C++ programming style. You know

int function1(int, int);
int function1(int x, int y)
{
int z = x + y;
return z;
}

If you want to do Cocoa programming with Objective-C i recommend a book by Aaron Hillegass... http://www.bignerdranch.com/products/cocoa1.shtml

very good book.. i'm awaiting a more advanced book to come out as well... here's for hoping.

you can get xcode for free from developers.apple.com

i'm not sure what you mean about designing for the Mac platform? do you mean interface design, stuff like that? i really dont' know how to get into that stuff...