Cohesion refers to how closely related and focused the responsibilities of a class or module are.
High Cohesion = Good → Class does one thing well. Low Cohesion = Bad → Class tries to do too many unrelated things.
Example
class InvoicePrinter {
void printInvoice(Invoice invoice) { ... }
}class InvoiceUtils {
void printInvoice() { ... }
void sendEmail() { ... }
void saveToDatabase() { ... } // unrelated responsibilities
}Key Points
- Promotes single responsibility principle (SRP).
- Leads to easier maintenance, better readability and modular code.
- Improves reusability and testability.
Real-World Analogy
A coffee machine that only brews coffee = high cohesion. A coffee machine that also plays music, opens garage door and orders pizza = low cohesion.
Tip
If asked about clean code, class design or SRP, bring up cohesion as a key principle. High cohesion = focused, well-designed code.
Parent: _Design Principles