Figure 12.3 is an object diagram. This diagram shows two NSDate instances on the heap. The two variables now and later are part of the frame for the function main(). They point to the NSDate objects, as shown by the arrows.

Figure 12.3  Object diagram for TimeAfterTime

You’ve only seen one class thus far: NSDate. There are, in fact, hundreds of classes that come with iOS and Mac OS X. We’ll work with some of the more common ones in the coming chapters.