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Questions and Answers
What is the primary purpose of a design in object-oriented design principles?
What is the primary purpose of a design in object-oriented design principles?
- To define the context of the program
- To implement concrete classes
- To create abstractions for inheritance
- To describe how something will work in a context using requirements (correct)
What principle is related to the idea of loose coupling?
What principle is related to the idea of loose coupling?
- The Dependency Inversion Principle (DIP)
- The Principle of Least Knowledge (PLK) (correct)
- The Interface Segregation Principle (ISP)
- The Liskov Substitution Principle (LSP)
What is the purpose of the Liskov Substitution Principle (LSP)?
What is the purpose of the Liskov Substitution Principle (LSP)?
- To define the context of the program
- To ensure clients depend on interfaces they use
- To create abstractions for inheritance
- To ensure subtypes are substitutable for their base types (correct)
What is the goal of the Dependency Inversion Principle (DIP)?
What is the goal of the Dependency Inversion Principle (DIP)?
What is the focus of the Interface Segregation Principle (ISP)?
What is the focus of the Interface Segregation Principle (ISP)?
What is an example of a design style in object-oriented design principles?
What is an example of a design style in object-oriented design principles?
What is the other name for the Principle of Least Knowledge (PLK)?
What is the other name for the Principle of Least Knowledge (PLK)?
What is the purpose of an interface in object-oriented design principles?
What is the purpose of an interface in object-oriented design principles?
What is the main cause of LSP violations in derived classes?
What is the main cause of LSP violations in derived classes?
What is the purpose of abstracting out common things in the DRY principle?
What is the purpose of abstracting out common things in the DRY principle?
What is the consequence of a sub-class throwing exceptions to hide certain behavior defined in its super class?
What is the consequence of a sub-class throwing exceptions to hide certain behavior defined in its super class?
What is the primary responsibility of a class according to the Single Responsibility Principle?
What is the primary responsibility of a class according to the Single Responsibility Principle?
What is the purpose of the Don't Repeat Yourself principle?
What is the purpose of the Don't Repeat Yourself principle?
What is an example of LSP violation in a sub-class?
What is an example of LSP violation in a sub-class?
What is the name of the principle that advises against duplicate code?
What is the name of the principle that advises against duplicate code?
What is the consequence of a class having multiple responsibilities?
What is the consequence of a class having multiple responsibilities?
What is the main idea behind the Dependency Inversion Principle?
What is the main idea behind the Dependency Inversion Principle?
What is the primary purpose of the design principles in object-oriented design?
What is the primary purpose of the design principles in object-oriented design?
What is a potential issue with deep inheritance trees?
What is a potential issue with deep inheritance trees?
What is the purpose of abstraction in object-oriented design?
What is the purpose of abstraction in object-oriented design?
What is the outcome of encapsulating things in your design that are likely to change?
What is the outcome of encapsulating things in your design that are likely to change?
What is the effect of exposing member data in public?
What is the effect of exposing member data in public?
What is an example of a class that remains relatively constant throughout the program?
What is an example of a class that remains relatively constant throughout the program?
What is the benefit of coding to an interface rather than to an implementation?
What is the benefit of coding to an interface rather than to an implementation?
What is the purpose of interfaces in object-oriented design?
What is the purpose of interfaces in object-oriented design?
What is the significance of the open triangle in a UML diagram?
What is the significance of the open triangle in a UML diagram?
What is the purpose of the Open-Closed Principle (OCP)?
What is the purpose of the Open-Closed Principle (OCP)?
What is the problem with data-only classes?
What is the problem with data-only classes?
What is an example of a class that implements the Shape interface?
What is an example of a class that implements the Shape interface?
What is the purpose of the Liskov Substitution Principle?
What is the purpose of the Liskov Substitution Principle?
What is the benefit of separating the features and methods of a class that remain relatively constant throughout the program from those that will change?
What is the benefit of separating the features and methods of a class that remain relatively constant throughout the program from those that will change?
What is an example of a feature that will change in the Violinist class?
What is an example of a feature that will change in the Violinist class?
When a class is used as part of another class but still exists outside of that class, what is this concept called?
When a class is used as part of another class but still exists outside of that class, what is this concept called?
What is the main idea behind the Principle of Least Knowledge?
What is the main idea behind the Principle of Least Knowledge?
What is the complement to strong cohesion in an application?
What is the complement to strong cohesion in an application?
What is the purpose of Delegation in object-oriented design principles?
What is the purpose of Delegation in object-oriented design principles?
What is the name of the principle that says 'high-level modules should not depend on low-level modules, but both should depend on abstractions'?
What is the name of the principle that says 'high-level modules should not depend on low-level modules, but both should depend on abstractions'?
What is the concept called when classes are related to each other?
What is the concept called when classes are related to each other?
What is the purpose of using Composition in object-oriented design principles?
What is the purpose of using Composition in object-oriented design principles?
Who introduced the 23 class design guidelines?
Who introduced the 23 class design guidelines?
Study Notes
Object-Oriented Design Principles
- Designs have a purpose: describe how something will work in a context, using the requirements (lists of features, user stories, and use cases) to define the context.
- Designs must have enough information: enough details in the design so that someone can come after you and implement the program correctly.
Fundamental Object-Oriented Design Principles
- Encapsulate things in your design that are likely to change: separate the features and methods of a class that remain relatively constant throughout the program from those that will change.
- Code to an interface rather than to an implementation: subtypes must be substitutable for their base types.
- The Open-Closed Principle (OCP): classes should be open for extension and closed for modification.
- The Don't Repeat Yourself (DRY) Principle: abstract out things that are common and place them in a single location to avoid duplicate code.
Other Design Principles
- The Liskov Substitution Principle (LSP): subtypes must be substitutable for their base types.
- The Dependency Inversion Principle (DIP): don't depend on concrete classes; depend on abstractions.
- The Interface Segregation Principle (ISP): clients shouldn't have to depend on interfaces they don't use.
- The Principle of Least Knowledge (PLK): talk only to your immediate friends.
Styles of Design
- Delegation: give responsibility for the behavior to another class.
- Composition: assemble behaviors from other classes.
- Association: classes are related to each other.
Class Design Guidelines
- 1. Don't expose member data in public.
- 2. Watch for coupling that's too tight (PLK).
- 3. Avoid deep inheritance trees (LSP).
- 4. Eliminate data-only classes.
- 5. Eliminate operation-only classes.
- 6. Avoid putting methods into the public interface.
- 7. Be sure to inherit only what you want to inherit (LSP).
- 8. Present a consistent level of abstraction in the class interface.
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Description
Understand the principles of object-oriented design, including the Liskov Substitution Principle and the Dependency Inversion Principle. Learn how to write code that is flexible and maintainable.
