Primitive Obsession
Most programming environments have two kinds of data. Record types allow you to structure data into meaningful groups. Primitive types are your building blocks. Records always carry a certain amount of overhead. They may mean tables in a database, or they may be awkward to create when you want them for only one or two things.
One of the valuable things about objects is that they blur or even break the line between primitive and larger classes. You can easily write little classes that are indistinguishable from the built-in types of the language. Java does have primitives for numbers, but strings and dates, which are primitives in many other environments, are classes.
People new to objects usually are reluctant to use small objects for small tasks, such as money classes that combine number and currency, ranges with an upper and a lower, and special strings such as telephone numbers and ZIP codes. You can move out of the cave into the centrally heated world of objects by using Replace Data Value with Object on individual data values. If the data value is a type code, use Replace Type Code with Class if the value does not affect behavior. If you have conditionals that depend on the type code, use Replace Type Code with Subclasses or Replace Type Code with State/Strategy.
If you have a group of fields that should go together, use Extract Class. If you see these primitives in parameter lists, try a civilizing dose of Introduce Parameter Object. If you find yourself picking apart an array, use Replace Array with Object.
