10 Questions
What is the primary benefit of design patterns?
Enabling large-scale reuse of software architectures
What is the main goal of reflection in design patterns?
To make classes self-aware and their behavior accessible for adaptation and change
What is the term for the property of a transaction that ensures it can be rolled back in case of failure?
Atomicity
What is the purpose of analysis patterns?
To provide reusable analysis models for various domains
What is the term for the structure and layers of a system design?
Architectural design
What is the benefit of using pattern names in developer communication?
It forms a common vocabulary
What is the term for the property of a transaction that ensures it maintains a consistent state?
Consistency
What is the main goal of design patterns in documenting systems?
To document expert knowledge and design tradeoffs
What is the term for the level of a system design that provides self-representation?
Meta-level
What is the purpose of design patterns in capturing expert knowledge?
To make it more widely available
Study Notes
Design Patterns
- Design patterns are not:
- Data structures that can be encoded in classes and reused as is (e.g., linked lists, hash tables)
- Complex domain-specific designs (for an entire application or subsystem)
- Design patterns are:
- Descriptions of communicating objects and classes that are customized to solve a general design problem in a particular context
Types of Patterns
- Creational patterns:
- Deal with initializing and configuring classes and objects
- Examples: Singleton, Abstract Factory, Builder, Factory Method, Prototype
- Structural patterns:
- Deal with decoupling interface and implementation of classes and objects
- Composition of classes or objects
- Examples: Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy
- Behavioral patterns:
- Deal with dynamic interactions among societies of classes and objects
- How they distribute responsibility
- Examples: Chain of Responsibility, Command, Interpreter, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor
Singleton Pattern
- Ensure that a class has only one instance and provide a global point of access to it
- Example: Singleton class with protected constructor and static instance
Structural Patterns
- Proxy:
- Acts as a convenient surrogate or placeholder for another object
- Types: Remote Proxy, Virtual Proxy, Protected Proxy
Behavioral Patterns
- Observer pattern:
- Intent: Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically
- Used in: Model-View-Controller framework, JDK's Abstract Window Toolkit (listeners), Java's Thread monitors, notify(), etc.
Patterns in Software Libraries
- AWT and Swing use Observer pattern
- Iterator pattern is used in C++ template library and JDK
- Facade pattern is used in many student-oriented libraries to simplify more complicated libraries
- Bridge and other patterns recur in middleware for distributed computing frameworks
Benefits of Design Patterns
- Enable large-scale reuse of software architectures and help document systems
- Explicitly capture expert knowledge and design tradeoffs and make it more widely available
- Help improve developer communication
- Pattern names form a common vocabulary
This quiz covers the basics of design patterns in software development, including intent, context, and consequences. It differentiates design patterns from data structures and complex domain-specific designs.
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