UML Class Diagrams Lecture

Introduction

• Instructor: Bear
• Topics Covered: Basic characteristics, relationships, examples

Basic Characteristics of Class Diagrams

• Class Representation:

  • Classes represent objects or entities in the system.
  • Depicted by a rectangular shape divided into three sections.

• Example: Zoo System

  • Class: Animal
    • Instance: Specific animal (e.g., Ruth)
    • Attributes: (middle section) – significant data for instances:
      • Name: name: String
      • ID: id: Integer
      • Age: age: Integer
    • Methods: (bottom section) – behavioral features of a class:
      • SetName: setName(name: String)
      • Eat: eat()

Visibility

• Determines the accessibility of attributes and methods
  • Private (-): Not accessible by other classes
  • Public (+): Accessible by other classes
  • Protected (#): Accessible by the same class and its subclasses
  • Package (~): Accessible by any class in the same package (rarely used)

Example: Employee Class

• Attributes:
  • Name name: String
  • Employee ID employeeID: Integer
  • Phone Number phoneNumber: Integer
  • Department department: String
• Method:
  • Update Phone Number updatePhoneNumber(newNumber: Integer)

Relationships Between Classes

Inheritance

• Concept: Subclasses inherit attributes and methods of a superclass.
• Example:
  • Superclass: Animal
  • Subclasses: Tortoise, Otter, Slow Loris
  • Inheritance Relationship: Open arrow between child (subclass) and parent (superclass).
  • Animal Class: Abstract (use italics or special notation).

Association

• Simple association relationship shown by a line.
• Example: Otter eats Sea Urchin.

Aggregation

• Whole-part relationship where parts can exist independently of the whole.
• Example:
  • Class: Creep (Group of Tortoises)
  • Relationship: Open diamond with Tortoise class.

Composition

• Strong whole-part relationship where parts cannot exist outside the whole.
• Example:
  • Class: Visitor Center
  • Parts: Lobby, Bathroom
  • Relationship: Closed diamond.

Multiplicity

• Numeric constraints on relationships.
  • One and only one: 1
  • One or many: 1..*
• Examples:
  • Visitor Center has one lobby (1)
  • Visitor Center has one or many bathrooms (1..*)
  • Other notations: 0..1, N, 0..*, 1..*, specific ranges.

Practical Example

• Scenario: Online Shopping Cart UML Diagram.
  • Class: User:
    • Attributes: userID, password, loginStatus, registerDate
    • Method: verifyLogin(): Boolean
  • Class Relationships:
    • Customer and Administrator inherit User.
    • Composition relationships: Customer and Shopping Cart, Orders, Shipping Info, Order Details.
  • Multiplicity:
    • Customer has zero or many orders (0..*).
    • Order belongs to one customer (1).
    • Order has one order detail (1).
    • Order Detail belongs to one order (1).*

Conclusion

• Tool Used: Lucidchart
• Further Learning: Visit training.lucid.co for more training on diagramming processes, systems, and organizations.