Proxy Pattern in Design Patterns

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Questions and Answers

What is the primary function of the Proxy Pattern?

To store data for quick access later

To simplify the interface of an existing object

To add an intermediary layer between a client and an actual object (correct)

To replace the original object with a different one

Which class represents the actual object that the client wants to access in the Proxy Pattern?

Real Subject Class (correct)

Subject Interface

Client Class

Proxy Class

Which of the following represents a practical use of the Proxy Pattern?

Providing logging and caching functionalities (correct)

Implementing an interface for multiple objects

Simplifying complex object interactions

Managing object creation and destruction

How does the Proxy Class interact with the RealSubject?

It delegates requests to the RealSubject while adding functionality Signup and view all the answers

What is one of the advantages of using the Proxy Pattern related to object creation?

It implements lazy initialization to create the object only when accessed Signup and view all the answers

What does the Proxy in the described scenario specifically check for before granting access?

User's location Signup and view all the answers

Which interface defines the methods and properties that the RealSubject and Proxy classes will implement?

Subject Interface Signup and view all the answers

Which locations are allowed by the proxy for access?

USA, Canada, and UK Signup and view all the answers

What role does the Client Class play in relation to the Proxy Class?

It is unaware of the Proxy Class and interacts only with the RealSubject Signup and view all the answers

What is the role of the `RealWebAccess` class?

To implement the <code>IWebAccess</code> interface and handle actual web access Signup and view all the answers

What does the LocationBasedWebAccessProxy specifically check before allowing access to a website?

The user's location Signup and view all the answers

How does the `LocationBasedWebAccessProxy` determine if access should be granted?

By using the <code>Array.Exists</code> method to check the allowed location list Signup and view all the answers

What happens if a user's location is not in the allowed list?

Access is denied and a message is printed Signup and view all the answers

What functionality does the `AccessWebsite` method of the `RealWebAccess` class provide?

Prints a message indicating website access from a location Signup and view all the answers

In what manner does the client code interact with the proxy?

It creates an instance of the proxy and tests accesses from various locations. Signup and view all the answers

What design pattern is illustrated by the implementation of `LocationBasedWebAccessProxy`?

Proxy Pattern Signup and view all the answers

Study Notes

Proxy Pattern

A design pattern providing a surrogate or placeholder for another object, controlling access.
Aims to add intermediary layers between clients and objects, for functionality, security or performance improvements.
Real-world examples include access control, logging, caching, and remote object access.

Proxy Pattern Structure

A Proxy class that implements the same interface as the original object.
A Real Subject class that represents the actual object being accessed.

Proxy Pattern Diagram

Subject Interface: Defines common methods and properties for both RealSubject and Proxy.
RealSubject Class: The actual object the client wants to access. Implements methods from the interface.
Proxy Class: Implements the same interface as the original object. Controls access to the RealSubject. This can intercept requests, add functionality or delegate to RealSubject.
Client: Interacts with the Proxy object and believes it's directly interacting with the RealSubject.

Advantages of Proxy Pattern

Access Control: The Proxy controls access to the RealSubject based on specific criteria.
Lazy Initialization: The Proxy can delay the creation of the RealSubject until it is needed, improving performance and reducing resource usage.

Example: Location-Based Website Access Proxy

A scenario where a proxy restricts website access based on user location.
A LocationBasedWebAccessProxy controls whether a website is accessible to a specific user based on their location.
The example involves a client, Proxy, and RealSubject objects, to control website access.
The output shows examples of how the method is working in a programming language (csharp) and demonstrates website access based on different user locations.

Step-by-Step Implementation (Example)

Step 1: Define the Subject Interface (IWebAccess). This defines the method for accessing websites along with URL and user location as parameters.
Step 2: Implement the Real Subject (RealWebAccess). This class implements the actual logic of accessing the websites.
Step 3: Implement the Proxy (LocationBasedWebAccessProxy). This class checks the user's location before allowing access.
Step 4: Client Code (example). This shows how a client could use the proxy for website access, demonstrating the access control logic.

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Description

Explore the Proxy Pattern, a crucial design pattern that acts as a surrogate or placeholder to control access to an object. This quiz covers its structure, including the relationships between the Proxy, Real Subject, and Client. Test your understanding of how this pattern can enhance functionality, security, and performance.