OOP Design Patterns

Question 1

What are Design Patterns in OOP?

Answer 1

Design patterns are reusable solutions to common software design problems. They provide proven approaches to structure code and improve maintainability, flexibility, and reusability.

Question 2

What are the different categories of Design Patterns?

Answer 2

Design patterns are typically categorized as Creational, Structural, and Behavioral. Creational patterns focus on object creation, Structural patterns on object composition, and Behavioral patterns on communication between objects.

Question 3

What is the Singleton Pattern?

Answer 3

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

Question 4

What is the Factory Method Pattern?

Answer 4

Creates objects without specifying the exact class to be instantiated.

Question 5

What is the Abstract Factory Pattern?

Answer 5

Provides an interface for creating families of related objects.

Question 6

What is the Builder Pattern?

Answer 6

Separates object construction from its representation, allowing step-by-step object creation.

Question 7

What is the Prototype Pattern?

Answer 7

Creates new objects by cloning an existing object.

Question 8

What is the Adapter Pattern?

Answer 8

Allows incompatible interfaces to work together by wrapping an object with an adapter interface.

Question 9

What is the Proxy Pattern?

Answer 9

Provides a surrogate or placeholder for another object to control access or add additional functionality.

Question 10

What is the Decorator Pattern?

Answer 10

Adds new functionality to an object dynamically without altering its structure.

Question 11

What is the Facade Pattern?

Answer 11

Provides a simplified interface to a complex system or a set of classes.

Question 12

What is the Composite Pattern?

Answer 12

Treats a group of objects as a single object, allowing for composing parts into a tree structure.

Question 13

What is the Strategy Pattern?

Answer 13

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

Question 14

What is the Observer Pattern?

Answer 14

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

Question 15

What is the Command Pattern?

Answer 15

Encapsulates a request as an object, allowing for parameterizing clients with different requests, queuing or logging requests, and undo/redo functionality.

Question 16

What is the Template Method Pattern?

Answer 16

Defines the skeleton of an algorithm in an operation, deferring some steps to subclasses.

Question 17

What is the Iterator Pattern?

Answer 17

Provides a way to access the elements of an object collection sequentially without exposing its underlying representation.

Question 18

What is the State Pattern?

Answer 18

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

Question 19

What is the Memento Pattern?

Answer 19

Without violating encapsulation, captures and externalizes an object’s internal state so it can be restored later.

Question 20

When to Use Design Patterns?

Answer 20

Use design patterns when you encounter recurring problems and need a proven, flexible solution. They are not a silver bullet and should be applied thoughtfully to avoid over-engineering.

Question 21

Situation: Only one “Settings” object needed in your app for global access.

Answer 21

Singleton Pattern - Ensures a single “Settings” instance exists for app-wide configuration access.

Question 22

Situation: Deciding between creating a “Button” or a “Dropdown” based on user input.

Answer 22

Factory Method Pattern - Hides button/dropdown creation logic, allowing for flexible UI element generation based on user choice.

Question 23

Situation: Integrating an old “Music Player” library with a new system that uses different controls.

Answer 23

Adapter Pattern - Acts as a bridge, allowing the new system to work with the old “Music Player” library despite incompatible interfaces.

Question 24

Situation: Adding new functionalities (like encryption) to an existing “Email” object without modifying its core functionality.

Answer 24

Decorator Pattern - Lets you dynamically add encryption functionality to the “Email” object without changing its core logic.

Question 25

Situation: Simplifying user interaction with a complex e-commerce “Shopping Cart” system.

Answer 25

Facade Pattern - Creates a simplified “Cart” interface that hides the complexities of managing items, discounts, and checkout within the shopping cart system