Replace Conditional with Polymorphism

Removes smells

Repeated Switches

Primitive Obsession

Referenced by patterns

Factory Method

Composite

Chain of Responsibility

Introduce Null Object

Introduce Polymorphic Creation With Factory Method

Replace Conditional Dispatcher With Command

Replace Conditional Logic with Strategy

Replace One/Many Distinctions With Composite

Replace State-Altering Conditionals with State

HumanAgent

Compare

Symptom

The same switch (or if/else chain) over a type code appears in multiple places — adding a new case means hunting them all down.

Goal

Each case becomes a class implementing a shared interface; dispatch happens once via virtual call.

Before the refactoring

switch (event.kind) {
  case 'click': return onClick(event);
  case 'key':   return onKey(event);
}

After the refactoring

event.handle(); // ClickEvent and KeyEvent each implement handle()

Example source: Illustrative example written for this site, not a quotation from any source.

Pressure

Dispatch logic duplicates across files; new cases are easy to miss; the type-code coupling amplifies with every additional consumer.

Tradeoff

If only one switch on the type code exists, polymorphism is overkill — wait for the second or third repeat before extracting subclasses.

Relief

Adding a new case is one new class; the type system surfaces what's missing.

Trap

Polymorphism worship — a switch with two stable cases becomes a class hierarchy of two trivial subclasses, paying class-hierarchy overhead with no flexibility return.