Stage 1 · Lesson 4 of 8
Inheritance, used sparingly
lets a subclass take on the fields and methods of a parent class and add to or override them. It models an is-a relationship: a SavingsAccount is an Account. Used for a true is-a, one or two levels deep, it keeps related types consistent and lets a subclass be used wherever the parent is expected.
The problems start when inheritance is used just to reuse code. A subclass is tied to every detail of its parent, so a change in the parent can quietly break it. This is often called the fragile base class problem. Deep hierarchies also make it hard to know where a method really comes from.
Common trapStack extends ArrayList style reuse, which leaks every list method to callers and can never be undone without breaking them.
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Resources for this stage
Start with· follow one of these
- CoursePaidGrokking the Object Oriented Design Interview
Design Gurus · Intermediate · Subscription
Its opening chapters teach the four OOP ideas applied inside real designs, with UML and running code
- CourseFreeMIT 6.102: Software Construction
MIT · Intermediate
Free MIT readings: Abstract Data Types, Rep Invariants and Interfaces and Subtyping are this stage at university depth