Design Pattern Glossary (OOD)

Common design patterns used in Object-Oriented Design interviews to solve recurring problems.

Creational Patterns

How objects are created.

• Factory Pattern: used in Chess Game to create pieces without specifying their concrete classes.
• Singleton Pattern: used in the Elevator System for the system controller to ensure only one instance handles dispatching.

Structural Patterns

How objects are composed.

• Composite Pattern: used in the File System to treat files and directories uniformly.
• Decorator Pattern: used in the Online Shopping System for adding shipping options (insurance, express) to an order.

Behavioral Patterns

How objects communicate.

• State Pattern: used in Vending Machine and ATM System to manage complex lifecycles.
• Strategy Pattern: used in Parking Lot for different pricing algorithms and Online Shopping for payment methods.
• Observer Pattern: used in Stack Overflow for notifying users of new activity.

[!TIP] Don't over-engineer! Apply patterns only when they solve a specific problem like "handling many if-else blocks" or "decoupling providers."