Question

Write a Quoteservice that works in either a push or pull model: define an operation to allow clients to register and receive Quotes (push) and define another operation to return a Quote for a specific Symbol (pull). Write a test client that gets pushed by the server and also pulls Quotes from the server.

Short answer

Create a `QuoteService` with push and pull methods, implement a `TestClient` to test both features.

Step-by-step solution

Define the QuoteService Class

Start by defining a class called `QuoteService`. In this class, you'll keep track of registered clients and offer operations for both the push and pull models of communication.

Implement the Push Model

Create a method `register_client` that takes a client object or identifier as a parameter and adds it to a list of registered clients. Then, define another method `push_quote` that iterates through this list and sends a quote to each client.

Implement the Pull Model

Add a method `get_quote(symbol)` to the `QuoteService` class. This method should take a stock symbol as an argument and return the corresponding quote.

Create a Test Client for Pushing Quotes

Define a `TestClient` class that has a method to receive a pushed quote from the `QuoteService`. This method will simulate a client receiving messages from the service.

Create a Test Client for Pulling Quotes

Extend the `TestClient` class with a method that explicitly calls `get_quote(symbol)` from the `QuoteService`. This simulates a client requesting a quote for a specific symbol.

Test the Complete Implementation

Instantiate the `QuoteService` and the `TestClient`. Register the client with the service, manually call the `push_quote` method to simulate a push, and use the `get_quote(symbol)` method for simulating pull operations.

Key concepts

Object-Oriented Design

Object-oriented design (OOD) is a programming paradigm that relies on the concept of "objects," which can contain data and code: data in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods). In Java programming, designing with objects helps structure an application logically. Every piece of functionality is represented by a class or an object.

In the exercise, the `QuoteService` and `TestClient` classes demonstrate object-oriented design principles. Each class encapsulates its own functionality and manages its own state. Through methods like `register_client`, `push_quote`, and `get_quote`, these classes provide a clear interface for interaction.

Utilizing object-oriented design leads to:

• Reusability - Objects and classes can be reused across different programs.
• Scalability - New functionality can be easily added by creating new classes.
• Maintainability - Changes in one part of the application can be made independently of others.
• Encapsulation - Keeping the internal state of objects hidden from the outside world protects the data.

Client-Server Architecture

Client-server architecture is a computing model that divides the system into two main parts: the client and the server. The server hosts, delivers, and manages most of the resources and services to be consumed by the client. The client requests these services from the server.

In the exercise, the `QuoteService` acts as the server providing quotes, whereas the `TestClient` is the client consuming these services. The server can either push quotes to the client, or the client can pull quotes from the server whenever needed. This model facilitates efficient resource management and enables multiple clients to interact with a single central server.

Key aspects of the client-server architecture include:

• Scalability - Additional clients can seamlessly interact with the server.
• Centralized Management - Server updates and maintenance are simpler since changes are made in one place.
• Security - Centralized data can be secured more effectively.
• Resource Sharing - Clients can share resources managed by the server, leading to better resource utilization.

Software Testing

Software testing is a process of evaluating and verifying that a software program or application does what it is supposed to do. It ensures the product is ready for consumption without defects and meets the specified requirements. There are several stages and types of testing, such as unit testing, integration testing, system testing, and acceptance testing.

In the context of the exercise, creating a `TestClient` to simulate interaction with the `QuoteService` is a crucial step in testing. This helps validate whether the `push` and `pull` operations are working as intended. Testing helps catch errors early and ensures reliability.

Benefits of comprehensive software testing include:

• Quality Assurance - Helps deliver high-quality software products.
• Cost Efficiency - Identifying and fixing defects early can reduce overall project costs.
• Customer Satisfaction - Well-functioning software meets user expectations, leading to satisfaction.
• Reliability - Ensures software behaves consistently under expected conditions.

Method Implementation

Method implementation refers to providing the actual code for a function or procedure defined in an interface or abstract class. It involves detailing how a certain task will be carried out within a program. Methods encapsulate functionality and allow developers to use and reuse code efficiently.

In Java, the `QuoteService` provides several method implementations such as `register_client`, `push_quote`, and `get_quote`. These methods define the logic for registering clients, pushing quotes, and retrieving specific quotes based on symbols. Implementing methods requires a clear understanding of the task and desired outcome.

Important considerations for method implementation include:

• Clarity - Ensure the method's purpose is evident from its name and comments.
• Simplicity - Keep methods simple and focused on a single task.
• Consistency - Follow consistent coding conventions for readability.
• Modularity - Break down complex tasks into smaller, manageable methods.