Question

Which of the following are applications of design patterns? Explain your conclusions. (a) An object-orientated design (b) The ability to vary the order in which a print() method is applied to the elements of a Vector (c) Varying the order in which a method is applied to the elements of a collection of objects by introducing a class whose methods include a method like goToNextElement() (d) Capturing the mutual behavior of a pair of objects of two classes (e) Capturing the mutual behavior of a pair of objects of two classes by introducing a third class aggregating the two classes

Short answer

Options (c) and (e) are applications of design patterns.

Step-by-step solution

Define Design Patterns

Design patterns are general, reusable solutions to common problems that arise during software design and development. They are templates designed to help write efficient, maintainable, and scalable code by providing a proven approach.

Analyze Each Option

We need to examine each given option (a-e) and determine if it fits the criteria for being a 'design pattern.' A design pattern should demonstrate a reusable solution with a defined strategy to a recurring problem.

Evaluate Option (a)

Option (a) describes an object-oriented design. While object-oriented design uses principles that underpin some design patterns, it is not itself a design pattern but rather a paradigm or style of programming.

Evaluate Option (b)

Option (b) is about varying the order of a method applied to elements of a Vector. This scenario doesn't describe a design pattern because it lacks the generalized template or strategy applicable to other similar problems.

Evaluate Option (c)

Option (c) involves introducing a class with a method like goToNextElement() to vary order. This aligns with the Iterator pattern, which is a design pattern that provides a way to access elements of a collection sequentially without exposing the underlying structure.

Evaluate Option (d)

Option (d) describes capturing the behavior between two class objects. This situation doesn't entail a typical design pattern structure as there's no mention of an abstraction, interface, or template to solve a broader issue.

Evaluate Option (e)

Option (e) involves creating a third class that aggregates two classes to capture their mutual behavior. This resembles the Mediator pattern, where an additional class encapsulates interaction logic between classes.

Conclusion Inference

Options (c) and (e) can be considered examples of design patterns. Option (c) relates to the Iterator pattern by introducing a navigation method, while option (e) aligns with the Mediator pattern by facilitating communication through an intermediary class.

Key concepts

Object-Oriented Design

Object-Oriented Design (OOD) is a programming paradigm that emphasizes the use of "objects" to represent data and methods. While not a design pattern itself, it's a foundation on which numerous design patterns are built. OOD revolves around four main principles:

• Encapsulation: Bundling data and methods that work on that data within one unit.
• Abstraction: Hiding complex realities while exposing only the necessary parts.
• Inheritance: Allowing new objects to take on the properties of existing objects.
• Polymorphism: Giving different objects the ability to be treated as instances of the same class through a common interface.

Objects in OOD model real-world entities, making code more intuitive and closely aligned with user requirements. This paradigm is essential in the architecture of many design patterns, which provide structured, reliable solutions to common problems.

Iterator Pattern

The Iterator Pattern is a design pattern that allows traversal of elements within a collection without exposing its underlying representation. It's like having a remote control to navigate a playlist without needing to access the playlist's complex structure.

Here's why it's beneficial:

• Separation of concerns: The pattern separates the traversal logic from the collection itself.
• Simplicity: Users can easily navigate through the elements without understanding the internal details.
• Flexibility: Different iteration methods can be implemented, such as forward and backward iteration.

The Iterator Pattern is widely used in OOD, supporting a consistent way to access collection elements regardless of the collection type. Introducing methods like `goToNextElement()` aligns with this pattern, ensuring streamlined access and control.

Mediator Pattern

The Mediator Pattern is a design pattern that facilitates communication between different components of a system by introducing a mediator object. This pattern helps reduce the complexity and dependencies in an application by organizing communication centrally. Think of it as a flight control tower that orchestrates communication between airplanes. Components communicate through the mediator rather than directly.

• Decoupling: The pattern helps decouple components, limiting dependencies.
• Flexibility: Changes to the system become easier, as only the mediator needs adjusting.
• Maintaining clarity: Complex interactions are easier to manage because the mediator clearly defines communication.

The use of an additional class to handle interactions between two class objects aligns with the Mediator Pattern, as seen in option (e). This central communication point eases system comprehension and evolution.

Software Design

Software Design is the process of defining the architecture, components, and interfaces of a system to satisfy specified requirements. It goes beyond programming by focusing on the overall structure and user experience of software. Key aspects include:

• Requirement Analysis: Understanding what the user needs from the system.
• Architecture Design: Creating the high-level structure of the system, including identifying major components.
• Component Design: Breaking down major components into smaller parts that are easier to implement and maintain.
• User Experience: Ensuring the software is not only functional but also user-friendly.

Effective software design relies heavily on design patterns, which provide tested and proven solutions for building systems. Adopting design patterns helps ensure that the software remains maintainable, scalable, and efficient while meeting the user's needs.