Smalltalk organizes all of its classes as a tree hierarchy. At the very top of this hierarchy is class Object. Following somewhere below it are more specific classes, such as the ones we’ve worked with—strings, integers, arrays, and so forth. They are grouped together based on their similarities; for instance, types of objects which may be compared as greater or less than each other fall under a class known as Magnitude.
One of the first tasks when creating a new object is to figure out where within this hierarchy your object falls. Coming up with an answer to this problem is at least as much art as science, and there are no hard-and-fast rules to nail it down. We’ll take a look at three kinds of objects to give you a feel for how this organization matters.