UML Class Diagrams

Class Diagrams

Overview

• A type of static structure diagram used in UML to describe the structure of a system
• Shows the classes, attributes, and operations of a system, as well as the relationships between them

Components of a Class Diagram

• Classes:
  • Represented by rectangles with three compartments: name, attributes, and operations
  • Can be abstract or concrete
• Attributes:
  • Data members of a class, represented by a list of variables inside the class rectangle
  • Can have data types, default values, and visibility (public, private, protected)
• Operations:
  • Methods or functions of a class, represented by a list of function signatures inside the class rectangle
  • Can have parameters, return types, and visibility (public, private, protected)

Relationships between Classes

• Inheritance:
  • Represented by a solid line with an open arrowhead, pointing from the subclass to the superclass
  • Indicates that a subclass inherits the attributes and operations of a superclass
• Association:
  • Represented by a solid line between two classes
  • Indicates that one class uses or references another class
• Aggregation:
  • Represented by a solid line with a diamond-shaped arrowhead, pointing from the container class to the contained class
  • Indicates that one class contains or composes multiple instances of another class
• Composition:
  • Represented by a solid line with a filled diamond-shaped arrowhead, pointing from the container class to the contained class
  • Indicates that one class contains or composes multiple instances of another class, and the contained class cannot exist independently

Additional Notations

• Multiplicity:
  • Indicated by a number or range of numbers near the association, aggregation, or composition line
  • Specifies the number of instances of one class that can be related to another class
• Role Names:
  • Indicated by a name or label near the association, aggregation, or composition line
  • Specifies the role or purpose of the relationship between the classes

Class Diagrams

Overview

• Describe the structure of a system using UML
• Show classes, attributes, and operations, as well as relationships between them

Components of a Class Diagram

Classes

• Represented by rectangles with three compartments: name, attributes, and operations
• Can be abstract or concrete

Attributes

• Data members of a class, listed inside the class rectangle
• Have data types, default values, and visibility (public, private, protected)

Operations

• Methods or functions of a class, listed inside the class rectangle
• Have parameters, return types, and visibility (public, private, protected)

Relationships between Classes

Inheritance

• Represented by a solid line with an open arrowhead, pointing from subclass to superclass
• Subclass inherits attributes and operations of superclass

Association

• Represented by a solid line between two classes
• One class uses or references another class

Aggregation

• Represented by a solid line with a diamond-shaped arrowhead, pointing from container to contained class
• One class contains or composes multiple instances of another class

Composition

• Represented by a solid line with a filled diamond-shaped arrowhead, pointing from container to contained class
• One class contains or composes multiple instances of another class, and the contained class cannot exist independently

Additional Notations

Multiplicity

• Indicated by a number or range of numbers near the association, aggregation, or composition line
• Specifies the number of instances of one class that can be related to another class

Role Names

• Indicated by a name or label near the association, aggregation, or composition line
• Specifies the role or purpose of the relationship between the classes

Class Diagrams

• UML Class Diagrams describe the structure of a system by showing classes, attributes, and relationships.

Elements of a Class Diagram

• Classes are represented by rectangles and can be abstract or concrete.
• Attributes are represented by compartments within the class rectangle and describe the properties of a class.
• Methods are represented by compartments within the class rectangle and describe the operations that can be performed on a class.
• Relationships are represented by lines connecting classes and describe the interactions between classes.

Types of Relationships

• Association describes a relationship between two classes where one class uses or depends on the other.
• Aggregation is a type of association where one class is a collection of objects of another class.
• Composition is a type of aggregation where the contained class cannot exist without the container class.
• Inheritance describes a relationship between a parent class and a child class, where the child class inherits the attributes and methods of the parent class.
• Dependency describes a relationship between two classes, where one class depends on the other, but not necessarily by association.

Notations

• A class is represented by a rectangle with three compartments: class name, attributes, and methods.
• An attribute is represented by a string in the format "name: type".
• A method is represented by a string in the format "name(parameters): return type".
• Relationships are represented by lines with arrowheads and labels.

Best Practices

• Use meaningful and descriptive names for classes, attributes, and methods.
• Keep the diagram simple and focused on the key elements of the system.
• Use notes and comments to provide additional information and context.
• Use stereotypes to extend the UML notation and provide additional information.