Design Patterns

Question 1

What is the Factory Pattern?

Answer 1

Provides an interface for creating objects, with subclasses deciding which class to instantiate.

Example: Pizza Factory

Question 2

What is the Singleton Pattern?

Answer 2

Ensures a class has only one instance and provides a global point of access to it.

Example: Logger Class

Question 3

What is the Observer Pattern?

Answer 3

Defines a one-to-many dependency between objects so that when one changes state, all its dependents are notified.

Example: Newsletter Subscription

Question 4

What is the Decorator Pattern?

Answer 4

Allows behavior to be added to individual objects without affecting the behavior of other objects from the same class.

Example: Coffee Shop (adding milk, sugar, etc.)

Question 5

What is the Adapter Pattern?

Answer 5

Converts the interface of a class into another interface that clients expect.

Example: Charging Adapter

Question 6

What is the Strategy Pattern?

Answer 6

Defines a family of algorithms, encapsulates each one, and makes them interchangeable.

Example: Payment Processing (Credit Card, PayPal)

Question 7

What is the Command Pattern?

Answer 7

Turns a request into a stand-alone object that contains all information about the request.

Example: Remote Control Buttons

Question 8

What is the Prototype Pattern?

Answer 8

Creates new objects by copying an existing object (prototype).

Example: Cloning a User Profile

Question 9

What is the Facade Pattern?

Answer 9

Provides a unified interface to a set of interfaces in a subsystem.

Example: Home Theater System (unifying controls for TV, sound, etc.)

Question 10

What is the Mediator Pattern?

Answer 10

Encapsulates how a set of objects interact, promoting loose coupling.

Example: Chatroom

Question 11

What is the Chain of Responsibility Pattern?

Answer 11

Passes a request along a chain of handlers until an object handles it.

Example: Customer Support (tiered escalation)

Question 12

What is the Builder Pattern?

Answer 12

Allows constructing complex objects step-by-step.

Example: Building a Meal (burger, drink, sides)

Question 13

What is the Template Method Pattern?

Answer 13

Defines the program skeleton in a method, deferring some steps to subclasses.

Example: Game Algorithm (setup, play, end)

Question 14

What is the State Pattern?

Answer 14

Allows an object to alter its behavior when its internal state changes.

Example: Vending Machine

Question 15

What is the Proxy Pattern?

Answer 15

Provides a surrogate or placeholder for another object.

Example: Virtual Proxy for Image Loading

Question 16

What is the Flyweight Pattern?

Answer 16

Reduces memory use by sharing as much data as possible with similar objects.

Example: Text Editor (sharing character objects)

Question 17

What is the Visitor Pattern?

Answer 17

Allows adding further operations to objects without modifying them.

Example: Tax Calculation on Various Items

Question 18

What is the Composite Pattern?

Answer 18

Composes objects into tree structures to represent part-whole hierarchies.

Example: File System (folders, files as tree structure)