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Module 2: Class & Sequence Diagrams
Module Overview
Unified Modeling Language (UML) diagrams are essential tools for visualizing and documenting software systems. In this module, you'll learn about class diagrams and sequence diagrams.
Learning Objectives
- Be able to create a class diagram showing:
- Properties
- Methods
- Access level
- Relationships between classes
- Understand the difference between types of class relationships:
- Association
- Aggregation
- Composition
- Be able to construct sequence diagrams for operations through an application, including:
- Method names
- Return types
- Alternate cases
- A list of participants
- Know how to read class and sequence diagrams for projects you did not design
Key Topics
UML Diagram Types
- Class diagrams
- Classes and objects
- Relationships (inheritance, composition, aggregation)
- Attributes and methods
- Access modifiers
- Sequence diagrams
- Actors and objects
- Messages and method calls
- Time flow
- Alternative flows
Practice Exercises
- Create a class diagram for a simple system
- Design a sequence diagram for a use case
- Document relationships between classes
- Model complex interactions
Next Steps
After completing this module:
- Complete the practice exercises above
- Review the additional resources for deeper understanding
- Move on to Module 3 to learn about Gradle
UML Diagrams Explained
UML (Unified Modeling Language) diagrams are standardized visual representations of a system's architecture, design, and behavior. They're essential tools for communicating software design concepts between team members.
Class Diagrams
Class diagrams provide a static view of the system by showing:
- Classes: Represented by rectangles divided into three sections (name, attributes, methods)
- Access Modifiers: Public (+), Private (-), Protected (#), Package (~)
- Relationships: How classes connect and relate to each other
Class Relationships
- Association: Basic relationship between classes (connected with a solid line)
- Aggregation: "Has-a" relationship where parts can exist independently (empty diamond)
- Composition: Stronger "Has-a" relationship where parts cannot exist without the whole (filled diamond)
- Inheritance: "Is-a" relationship where child classes inherit from parent (arrow pointing to parent)
Sequence Diagrams
Sequence diagrams show the flow of interactions between objects over time:
- Participants: Objects or actors in the system (shown as rectangles at the top)
- Lifelines: Vertical dashed lines representing object existence over time
- Messages: Arrows between lifelines showing method calls and responses
- Alternative Flows: Conditional paths in the sequence using alt/opt fragments
Benefits of UML Diagrams
- Clarify complex systems and interactions before coding begins
- Communicate design concepts to team members and stakeholders
- Document system architecture for future maintenance
- Identify potential issues early in the development cycle