Chapter 2: How to Read a Class Diagram

大綱

• What’s in a class diagram?

• Challenges

• Key points

What’s in a class diagram?

• “inherits from,” read this as “is a”

  • SheepDog is a Dog.

• a Farmer has one or more Dogs

• a Farmer has a SheepDog that’s a Dog

• Farmer conforms to PetOwning

• indicate that Dog delegates to a PetOwning object

• a Farmer that has a SheepDog, which is a Dog that delegates to a PetOwning object

  

Challenges

• Dog and Cat inherit from Animal, which defines an eat method.

• Vehicle protocol has one Motor and one or more Wheel objects.

• Professor is a Teacher and conforms to a Person protocol.

Key points

• Class diagrams give a visual representation of class and protocol types, showing their properties and methods.

• Class diagrams also show the relationship between the object types.

• Class diagrams can be drawn in any other orientation; the direction of the arrows define the meaning.

• Boxes denote classes, and lines denote relationships: “implements,” “has a,” “uses“ and “conforms to” are the most common relations.

• Boxes can also denote protocols, which is indicated by <> before the name.