Polymorphism

“How to handle alternatives based on type?” – Craig Larman

When related alternatives or behaviors vary by type (class), assign responsibility for the behavior—using polymorphic operations—to the types for which the behavior varies.

When to use

When you see a switch or if statement checking the type of an object to decide what to do.

Why it matters

Extensibility: You can add new types without modifying the main logic (OCP).
Simplicity: Eliminates massive switch/case blocks.

Signs of Violation

switch (type) { case 'A': ... case 'B': ... }
if (obj instanceof Dog) ... else if (obj instanceof Cat) ...

Explanation

Problem

Conditional logic based on type is fragile. If you add a new type, you have to find and update all those conditional blocks scattered across the system.

Solution

Use the language’s polymorphic features. Define a common interface and let each class implement its own version of the behavior.

Real world analogy

You don’t need to check “If it’s a Dog, say woof; if it’s a Cat, say meow”. You just say “Speak!”, and the animal does what is natural for its type.

Pros and Cons

Pros	Cons
Eliminates conditionals Supports OCP	Can be “overkill” for very simple, stable logic

Comparison

Strategy Pattern: A common way to implement polymorphism for algorithms.
Factory Pattern: Often used to create the polymorphic objects so the client doesn’t need to know the concrete type.