Instance class are not normally executable. That is they may contain lots of fields (attributes) and methods, but generally have no main() method. The technique we will use for the next few modules will be to have a companion driver class.

In the UML class diagram above you will see we added a separate class Driver, which has one method and no attributes.

The first thing you may notice is that the method is underlined. In UML, underlined class element are class-level attributes or objects. Each language may implement these differently, but in general to access a class element all one needs is the class name, so Driver.main() will generally call the class-method main() in the class Driver. Class-features can only be called by using the class name.

Next you may observe the dotted line arrow. This indicates that the class Driver depends on the class Ingredient. For our purposes this means:

• Ingredient must work correctly for Driver to work correctly
• Driver must include, use, import or somehow have access to Ingredient
  • We will cover how to do this for you specific language later in this module
• We anticipate that at least one method in Driver will make or access an Ingredient object.