Refactor: Dealing with Generalization

Overview

These 12 techniques manage inheritance hierarchies — pulling shared behavior up, pushing specific behavior down, extracting common interfaces, and replacing inheritance with delegation (or vice versa). Correct generalization prevents code duplication across subclasses while avoiding over-engineering.

When to Use

• Sibling classes share duplicate methods or fields
• Subclass only uses a fraction of parent's interface (Refused Bequest)
• Adding a subclass in one hierarchy requires adding one in another (Parallel Inheritance)
• Abstract class has only one concrete subclass (Speculative Generality)
• Inheritance used for code reuse rather than true is-a relationships

Quick Reference