objective-C 的Hello World!

Console視窗的運作結果：

2011-01-25 13:49:05.978 HelloWorld[734:a0f] drawing a circle at (0,0,10,30) in red

2011-01-25 13:49:06.016 HelloWorld[734:a0f] drawing a rectangle at (30,40,50,60) in green

2011-01-25 13:49:06.018 HelloWorld[734:a0f] drawing an egg at (15,18,37,39) in blue