Programming iOS 6, 3rd Edition

Objects

An object, in programming, is based on the concept of an object in the real world. It’s an independent, self-contained thing. These objects, unlike purely inert objects in the real world, have abilities. So an object in programming is more like a clock than a rock; it doesn’t just sit there, but actually does something. Perhaps one could compare an object in programming more to the animate objects of the real world, as opposed to the inanimate objects, except that — unlike real-world animate things — a programming object is supposed to be predictable: in particular, it does what you tell it. In the real world, you tell a dog to sit and anything can happen; in the programming world, you tell a dog to sit and it sits. (This is why so many of us prefer programming to dealing with the real world.)

In object-based programming, a program is organized into many discrete objects. This organization can make life much easier for the programmer. Each object has abilities that are specialized for that object. You can think of this as being a little like how an automobile assembly line works. Each worker or station along the line does one thing (screw on the bumpers, or paint the door, or whatever) and does it well. You can see immediately how this organization helps the programmer. If the car is coming off the assembly line with the door badly painted, it is very likely that the blame lies with the door-painting object, so we know where to look for the bug in our code. Or, if we decide ...