• Object-Oriented Programming is a paradigm that organizes code into objects.
• Objects contain data (attributes/properties) and code (methods/procedures) to manipulate that data.
• OOP is used for designing modular, reusable, and scalable applications.
• OOP is commonly used in languages like C#, Java, and Python.

Key Concepts of Object-Oriented Programming

• Classes and Objects
• Encapsulation
• Inheritance
• Abstraction
• Polymorphism

Classes and Objects

• A class is a blueprint for creating objects.
• An object is an instance of a class.

Encapsulation (Data Hiding)

• Encapsulation hides internal details but exposes data and methods via a public interface, preventing unintentional changes.
• It restricts direct access to object data.
• Encapsulation bundles data (variables) and the methods/functions that operate on it into a single unit, usually a class.

Abstraction (Hiding Complexity)

• Abstraction Reduces complexity by only surfacing the information needed for a given context or use case.
• Abstraction Hides implementation details and only shows essential features.
• Abstract everything needed and encapsulate everything not needed.

Inheritance (Code Reusability)

• Inheritance allows classes to inherit properties and methods.
• Inheritance makes code reusable and organized.
• A child class derives from a parent class.

Polymorphism (Multiple Forms)

• Polymorphism is a principle that enables objects to change their form.
• Polymorphism allows this by extending or overriding existing methods.
• Polymorphism means One interface, multiple implementations.

Introduction to UML

• UML is a standardized visual modeling language.
• UML visualizes, specifies, builds, and documents software system designs.
• UML assists software engineers, business analysts, and system architects in modeling, design, and analysis.
• UML diagrams are categorized into structural (e.g., class, object, component) and behavioral (e.g., use case, sequence, activity) types.
• UML helps represent and communicate complex system designs to promote collaboration.

Why is UML needed?

• UML Helps visually represents and communicate complex system designs, promoting understanding and collaboration.
• UML Bridges the gap between programmers and non-programmers, enabling businessmen to comprehend system requirements and processes.
• UML Visualizes processes interactions, and system structures mean teams save time and improve efficiency.

Types of UML

• Behavioral UML diagrams show the dynamic aspects of a system.
• Behavioral UML diagrams depict how objects interact and respond to events over time.
• Structural UML diagrams show the static aspects of a system and represent classes, objects, components, and their relationships to illustrate the system's architecture.

Common UML Diagrams

• Class Diagram
• Object Diagram
• Sequence Diagram
• Package Diagram

Class Diagram

• Most widely used UML diagram.
• Class Diagrams are the foundation of object-oriented systems.
• Depicts the static structure of a system by showing classes, their attributes, methods, and relationships.
• Class diagrams identify connections between different classes or objects and provide a graphical notation to construct and visualize object-oriented systems.

What is a Class?

• A class is a blueprint for an object, defining its properties and method
• Objects are usable instances of classes, created based on the class blueprint.
• Classes describe the type of objects, Objects represent actual instances with their own states and behaviors.

UML Class Notation

• A class represents a concept that encapsulates state (attributes) and behavior (operations).
• Attributes have types, and operations have signatures.
• The class name is the only mandatory information.
• The class name appears in the first partition of the UML class diagram.
• Attributes are listed in the second partition, including the attribute type following a colon (e.g., attributeName: dataType).
• Attributes correspond to member variables (data members) in code.
• Class operations/methods are shown in the 3rd partition of the diagram.
• Return Type is shown after the colon
• Parameters are also shown, using colon

Class Visibility

• Class visibility: +, -, and # symbols before names denote visibility of attribute/operation.
• • denotes public attributes or operations.
• - denotes private attributes or operations.

• denotes protected attributes or operations.

Parameter Directionality

• Each parameter in an operation/method may be denoted as in, out, or inout, specifying direction with respect to the caller.

Perspectives of Class Diagram

• The perspective depends on the development stage, influencing detail and relationships in the model.
• Conceptual represents the concepts in the domain.
• Specification focuses on the interfaces of Abstract Data Types (ADTs) in the software.
• Implementation describes how classes will implement their interfaces.

Relationships Between Classes

• UML is more than just visual representation
• UML can provide a precise blueprint for code implementation.
• The resulting code aligns with the designer's intent when accurately interpreted.
• Classes can have one or more relationships with other classes, of different types.

Inheritance (or Generalization)

• Generalization is a taxonomic "is-a" relationship
• It allows a subclass to inherit attributes/behaviors from a more general superclass, promoting abstraction and reusability.
• A subclass is also an instance of the superclass.

Association

• Associations are relationships between classes in a UML Class Diagram.
• They are represented by a solid line between classes.
• Associations are typically named using a verb or verb phrase.

Simple Association

• A structural link between peer classes.
• Cardinality expresses the numerical relationship between instances of classes.

Aggregation

• Aggregation is a special type of association.
• Aggregation represents a "part of" relationship
• Objects of the Class1 and Class2 can have separate lifetimes.
• Class2 is part of Class1

Composition

• Composition is a special type of aggregation: parts are destroyed when the whole is destroyed.
• Objects live and die with Class1.
• Class2 cannot stand by itself.

Dependency

• An object of one class might use an object of another class in the code of a method.
• This is a special type of association.
• Exists between two classes If changes to the definition of one may cause changes to the other (but not the other way around).

Realization

• Realization is a relationship between a blueprint class/interface and class that implements it.
• The implementing class provides the actual details, fulfilling the contract defined by the interface.

Object Diagram

• An Object Diagram: a snapshot of system's instances and their relationships at a specific moment.
• Object Diagram is the diagram that helps analyze system behavior by showing instantiated objects and their interactions.
• Object Diagrams show instances of classes in the system.

Package Diagram

• A Package Diagram illustrates the organization of packages and their elements.
• They show dependencies between packages and their internal composition.
• Packages help to organize UML diagrams into meaningful groups.
• Primarily used to organize class and use case diagrams.

Sequence Diagram

• A Sequence Diagram simply depicts interaction between objects in a sequential order.
• Sequence diagrams describe how and in what order the objects in a system.
• These diagrams are widely used by businessmen and software developers to document and understand requirements for new and existing systems.

Steps to Create UML Diagrams

• Define the objective (e.g., requirements gathering, system architecture, documentation).
• Choose key components (classes, objects, use cases) and their connections.
• Pick the appropriate diagram (e.g., class, use case, sequence, activity).
• Visualize the structure before using a UML tool.
• Select software for creating and editing UML diagrams.
• Add elements Use appropriate relationships.
• Specify attributes.

UML Diagram types to Practice

• Design a Class Diagram for Library Management System
• Design a Class Diagram applying the Relationships between Classes
• Design a Sequence Diagram for Online Shopping

Explore object-oriented programming (OOP) principles. Learn about objects containing data and code and how OOP is used for designing scalable applications. Key concepts include classes, objects, encapsulation, abstraction and polymorphism.