UML & Class Diagrams

The acronym UML stands for Unified Modeling Language. UML is a standardized visual modeling language used to provide a common way to visualize the design of software or systems. It helps developers, architects, and stakeholders specify, visualize, construct, and document the structure and behavior of software systems using a set of graphical diagrams

UML diagrams are divided into two main categories

• Structural Diagrams: Show the static structure of a system—its components, classes, objects, and their relationships.

• Behavioral Diagrams: Illustrate the dynamic aspects of a system—how components interact and behave over time.

Among all UML diagrams, the Class Diagram is the most widely used and fundamental in object-oriented design

Class Diagram

Static structure diagram in UML that represents the structure of a system by showing its classes, their attributes (properties), methods (operations), and the relationships between classes.

source

Each class is depicted as a rectangle divided into three compartments:

• Class Name: The top section, showing the name of the class.

• Attributes: The middle section, listing the properties or data fields.

• Methods: The bottom section lists the operations or functions the class can perform.

• Visibility:

  • + Public

  • - Private

  • # Protected

  • ~ Package

Class diagrams also illustrate various relationships between classes, such as:

• Association: A general connection between classes.

  • Example: A Student class is associated with a Course class, as a student can enroll in multiple courses.

• Aggregation: A "has-a" relationship where the part can exist independently.

  • Example: A Car class has an Engine class but the Engine class can exist without the Car class.

• Composition: A strong "has-a" relationship where the part cannot exist without the whole.

  • Example: A House class is composed of Room class but the Room class can not exist without the House class.

• Inheritance (Generalization): An "is-a" relationship where subclasses inherit from a superclass.

  • Example: A Dog class and a Cat class inherit from an Animal class, as both dogs and cats are animals.

• Implementation: An "is-a" relationship between a class and interface, where class implements the methods in the interface.

  • Example: A Rectangle class and a Circle class implement the Shape interface, which declares a getArea() method.

• Dependency: Indicates one class uses or depends on another.

  • Example: A Customer class uses an Order class to place order.

References:

UML Class Diagram Tutorial

https://blog.algomaster.io/p/uml-class-diagram-explained-with-examples