Refactoring Pattern 2: Extract Class

Learning Goals

• Explain Extract Class & how it promotes abstraction & single responsibility principle
• Identify scenarios for which Extract Class is the appropriate refactoring pattern to use
• Implement Extract Class

Supplies

• You should have a copy of this extraction of Chapter 7.

First 12 minutes individually:

• Briefly read the Extract Class section from 175 to 179
• Carefully re-read the code sections on 177 and 178
• Reflect on these key ideas of Extract Class:
  • One object is doing the work of two (or more)
    • This is one of the most common weaknesses in object-oriented systems
  • Really is a “Step 1” before applying Move Method
  • Allows for easier testing, reuse, and abstraction
• Try refactoring this example scenario (you should already have this cloned) using Extract Class. As you create new classes and move things around, make sure the linked test still passes
• If you finish early, apply this refactoring pattern to the Enigma examples found under Additional Resources in the main lesson for today
• If you still have more time, apply this refactoring pattern to your current project

Final 3 minutes in your small group:

• Answer the following questions:
  • When would you decide to extract a class?
  • What benefits does extracting a class provide you as a programmer?
  • Should you move methods first or extract classes first?
• Compare solutions