OBJECT ORIENTED ANALYSIS AND DESIGN GRASP: Designing Objects with Responsibilities: Object Design: Example Inputs, Activities and Outputs, Responsibilities and Responsibility-Driven Design, GRASP: A Methodological Approach to Basic OO Design, the Connection between Responsibilities, GRASP and UML Diagrams, Patterns, A Short Example of Object Design with GRASP Designing for Visibility: Visibility between Objects Mapping Designs to Code: Creating Class Definitions from DCDs, Creating Methods from Interaction Diagrams, Collection Classes in Code

 

Introduction To All Topics of unit 5 in Object Oriented Analysis And Design

GRASP: Designing Objects with Responsibilities: Object Design: Example Inputs, Activities and Outputs, Responsibilities and Responsibility-Driven Design, GRASP: A Methodological Approach to Basic OO Design, the Connection between Responsibilities, GRASP and UML Diagrams, Patterns, A Short Example of Object Design with GRASP Designing for Visibility: Visibility between Objects Mapping Designs to Code: Creating Class Definitions from DCDs, Creating Methods from Interaction Diagrams, Collection Classes in Code

Introduction to Object-Oriented Analysis and Design Topics

1. GRASP: Designing Objects with Responsibilities

In object-oriented design, the principle of assigning responsibilities to objects effectively is fundamental for creating maintainable and scalable systems. GRASP (General Responsibility Assignment Software Patterns) provides a set of guidelines and patterns to aid designers in determining which object should be responsible for which behavior.

GRASP patterns include Creator, Controller, Information Expert, Low Coupling, High Cohesion, Polymorphism, Indirection, and Protected Variations. These patterns help designers make informed decisions about system architecture and object interactions.

For instance, the Information Expert pattern suggests that a class should be responsible for performing tasks that require knowledge of its own data. This promotes encapsulation and prevents data from being scattered across multiple classes.

2. Object Design: Example Inputs, Activities, and Outputs

Object design involves a detailed analysis of system requirements to identify the inputs, activities, and outputs associated with each object. Inputs represent the data or signals received by an object, which can originate from users, external systems, or other objects within the system.

Activities represent the processes or operations performed by an object in response to inputs. These activities may involve calculations, validations, data transformations, or interactions with other objects.

Outputs are the results or responses generated by an object as a result of its activities. Outputs can take various forms, such as displaying information to users, triggering events, updating data, or passing information to other objects.

3. Responsibilities and Responsibility-Driven Design

Responsibility-driven design is a fundamental principle in object-oriented analysis and design. It emphasizes identifying the responsibilities of each object in a system and designing them accordingly.

Responsibilities can include behaviors, attributes, or collaborations with other objects. By focusing on responsibilities, designers create objects that are cohesive, loosely coupled, and easy to maintain. This approach fosters a clear understanding of the system's architecture and promotes modularity and reusability.

For example, in a banking system, a Customer object might have responsibilities such as makeDeposit, makeWithdrawal, and checkBalance, while a BankAccount object might have responsibilities such as debit, credit, and calculateInterest.

4. GRASP: A Methodological Approach to Basic OO Design

GRASP provides a systematic approach to basic object-oriented design by offering guidelines and principles to assist designers in making informed decisions. These principles help in determining object responsibilities, defining collaborations between objects, and structuring class hierarchies.

For example, the Creator pattern suggests that a class should be responsible for creating instances of related classes. This helps in maintaining low coupling between classes and ensures that changes in one class do not cascade to other classes.

The Controller pattern advocates for a separate controller object to manage the flow of communication between objects in a system. This promotes flexibility and modularity by centralizing the decision-making logic.

5. The Connection between Responsibilities, GRASP, and UML Diagrams

Unified Modeling Language (UML) diagrams serve as visual representations of object-oriented designs, illustrating the structure, behavior, and interactions of objects within a system.

There exists a strong connection between responsibilities, GRASP principles, and UML diagrams. GRASP guides the assignment of responsibilities, which are then represented in various types of UML diagrams, such as class diagrams, sequence diagrams, and collaboration diagrams.

For example, in a class diagram, classes are depicted along with their attributes and methods, reflecting the responsibilities assigned to each class. Sequence diagrams illustrate the flow of messages between objects over time, showing how responsibilities are fulfilled through object interactions.

6. Patterns

Design patterns are reusable solutions to common problems encountered in software design. They encapsulate best practices and proven solutions that can be applied to various design problems.

Patterns address recurring design challenges, such as managing dependencies, enhancing flexibility, and improving code maintainability. By understanding and applying patterns, designers can leverage existing solutions to design robust, scalable, and maintainable software systems.

Popular design patterns include Singleton, Factory, Observer, Decorator, and Strategy. Each pattern addresses specific design concerns and provides a blueprint for implementing common solutions.

7. A Short Example of Object Design with GRASP

Let's consider a simplified example of a restaurant management system to demonstrate how GRASP principles are applied in object-oriented design.

In this system, we have objects such as Order, Menu, Table, and Chef. Applying GRASP principles:

• Information Expert: The Order object is responsible for managing order details, while the Menu object is responsible for storing menu items.
• Low Coupling: The Order object communicates with the Chef object to prepare dishes, but it doesn't need to know the internal workings of the Chef.
• High Cohesion: The Table object manages table-related operations, such as seating guests and processing payments, without interfering with other objects' responsibilities.

Through this example, we can see how applying GRASP principles results in a well-structured and modular design that is easy to understand and maintain.

8. Designing for Visibility: Visibility between Objects

Visibility between objects refers to the ability of one object to access or interact with another object. Properly managing visibility is essential for creating robust and maintainable object-oriented systems.

Designing for visibility involves determining the appropriate level of access between objects to achieve the desired behavior while maintaining system integrity. This includes considering factors such as encapsulation, information hiding, and modularity.

For example, in a banking system, the Account object may have methods for depositing and withdrawing funds, but these methods should be appropriately encapsulated to prevent unauthorized access or modification.

9. Mapping Designs to Code: Creating Class Definitions from DCDs

Design Class Diagrams (DCDs) provide a high-level view of the static structure of a system, depicting classes, attributes, methods, and their relationships.

Mapping DCDs to code involves translating these diagrams into actual class definitions in a programming language, such as Java or C++. This process requires careful consideration of design principles, coding standards, and best practices.

For example, a DCD depicting a Customer class with attributes like name and email would be translated into a corresponding Java class with member variables and accessor methods.

10. Creating Methods from Interaction Diagrams

Interaction diagrams, such as sequence diagrams and collaboration diagrams, depict how objects interact with each other over time to achieve a specific behavior or functionality.

From these diagrams, designers can derive the methods and operations that need to be implemented in each class to realize the desired behavior. This involves analyzing the sequence of interactions and identifying the responsibilities of each object.

For instance, a sequence diagram depicting a customer purchasing an item online would lead to the creation of methods such as addToCart, processPayment, and updateInventory in relevant classes.

11. Collection Classes in Code

Collection classes represent groups of related objects, such as lists, sets, or maps. They are essential for managing data efficiently in object-oriented systems.

Implementing collection classes in code involves selecting appropriate data structures, algorithms, and design patterns to ensure optimal performance and maintainability.

For example, a collection class like ArrayList in Java provides dynamic arrays that can grow as needed, while a HashMap allows efficient key-value pair storage and retrieval.

12. Designing Objects with Responsibilities

Designing objects with clear responsibilities is crucial for creating maintainable and efficient object-oriented systems. Each object should have a well-defined purpose and should be responsible for a specific set of tasks.

When designing objects, it's essential to consider the Single Responsibility Principle (SRP), which states that a class should have only one reason to change. This principle helps in creating cohesive and loosely coupled objects, making it easier to maintain and extend the system.

For example, in a messaging application, a Message object may be responsible for storing message content, sender information, and timestamp, while a Notification object may handle the delivery of messages to users' devices.

13. Applying GRASP Principles

Applying GRASP (General Responsibility Assignment Software Patterns) principles is essential for achieving a well-designed object-oriented system. These principles guide designers in making informed decisions about the assignment of responsibilities to objects.

Some common GRASP principles include Creator, Low Coupling, High Cohesion, and Indirection. By applying these principles, designers can create systems that are flexible, maintainable, and easy to understand.

For instance, the Creator principle suggests that a class should be responsible for creating instances of related classes, promoting loose coupling between objects and enhancing code maintainability.

14. UML Diagrams in Object-Oriented Design

Unified Modeling Language (UML) diagrams are graphical representations used to visualize and communicate object-oriented designs. They provide a standardized way to depict the structure, behavior, and interactions of systems.

Common types of UML diagrams used in object-oriented design include Class Diagrams, Sequence Diagrams, Collaboration Diagrams, and State Diagrams. Each type of diagram serves a specific purpose in the design process.

For example, a class diagram illustrates the static structure of a system by showing classes, attributes, methods, and relationships between classes. On the other hand, a sequence diagram depicts the dynamic interactions between objects over time.

15. Design Patterns and Anti-Patterns

Design patterns are proven solutions to common problems encountered in software design. They provide reusable templates for solving recurring design challenges and promoting best practices in system architecture.

On the other hand, anti-patterns are common pitfalls or bad practices that should be avoided in software design. Recognizing and avoiding anti-patterns is essential for creating robust and maintainable systems.

Examples of design patterns include Singleton, Factory, Observer, and Decorator, while examples of anti-patterns include God Object, Spaghetti Code, and Golden Hammer.