Curso POO Teoria #03a - O que é Visibilidade em um Objeto?

Introduction to Object-Oriented Programming

Welcome and Course Overview

• The instructor welcomes students to another lesson in the Object-Oriented Programming course.

• Gustavo Guanabara introduces himself as the professor and mentions that this is the third class, focusing on visibility in programming.

Importance of Visibility

• Understanding visibility is crucial for grasping the essence of object-oriented programming.

• The Unified Modeling Language (UML) is introduced; it’s important but not the main focus of this course.

Unified Modeling Language (UML)

Overview of UML

• While UML won't be deeply covered, it's essential for understanding object-oriented concepts.

• The class diagram is highlighted as a key component of UML that students will encounter in their studies.

Class Diagrams Explained

• Class diagrams represent objects like a pen, simplifying complex models into rectangles.

• Each class is represented as a rectangle, with attributes and methods clearly defined within it.

Class Representation

Structure of Classes

• A car or any other object can also be represented similarly using rectangles in UML.

• The top part of the rectangle contains the class name, while attributes are listed below it.

Attributes and Methods

• Attributes are characteristics of classes; methods define behaviors.

• Attributes start with lowercase letters while methods begin with uppercase letters followed by parentheses.

Modifiers of Visibility

Introduction to Visibility Modifiers

• There are three visibility modifiers: public (+), private (-), and protected (#).

• These modifiers indicate access levels to internal components (attributes and methods).

Understanding Access Levels

Understanding Public, Private, and Protected Attributes in Object-Oriented Programming

Introduction to Visibility Concepts

• The instructor emphasizes the importance of natural explanations in teaching programming concepts, recalling a previous lesson focused on simplicity and practical examples.

• A relatable analogy is introduced using everyday objects like telephones to explain the differences between public, private, and protected attributes.

Public vs. Private vs. Protected Attributes

• Public Attribute: Defined as accessible by anyone; for example, a public phone can be used by anyone who finds it.

• Private Attribute: Refers to personal items like a mobile phone that only the owner can access; it requires security measures such as passwords or biometric locks.

• Protected Attribute: Illustrated with a home phone scenario where only family members or authorized individuals can use it; this concept is crucial for understanding class relationships.

Definitions in Object-Oriented Programming

• Recap of definitions:

• Public: Accessible by all classes.

• Private: Accessible only within the defining class.

• Protected: Accessible within the defining class and its subclasses.

Class Structure and Visibility

• The instructor transitions into discussing how these visibility levels apply in object-oriented programming (OOP), particularly focusing on attributes and methods defined within classes.

• An explanation follows about how private attributes limit access strictly to their own class while public attributes allow broader accessibility across different classes.

Practical Application with Class Diagrams

• The discussion moves towards visual representation through class diagrams, highlighting how visibility symbols are integrated into attribute definitions.

• A specific example is given with a "Pen" class diagram that includes various attributes along with their respective visibility levels (public/private/protected).

Defining Attributes and Methods

• The instructor outlines how to define attributes within a class structure while specifying their visibility clearly at the beginning of each definition.

• Two methods are introduced—writing and doodling—both marked as public, demonstrating how method visibility aligns with attribute visibility principles.

Understanding Visibility in Object-Oriented Programming

The Importance of Visibility

• Visibility is crucial in programming, affecting how attributes and methods can be accessed. Each programming language has a default visibility setting.

• An example is provided with the class "caneta" (pen), illustrating how to create an object from this class using the syntax objectName = new ClassName().

• The speaker emphasizes the importance of understanding object creation, suggesting revisiting previous lessons if needed.

Accessing Attributes Based on Visibility

• Attributes defined as public can be accessed freely; for instance, a public attribute "modelo" allows modification without restrictions.

• In contrast, private attributes like "ponta" cannot be modified directly outside their defining class, leading to invalid operations when attempted.

Protected and Private Attributes

• A protected attribute like "carga" can only be accessed by subclasses or within its own class. Attempts to modify it from outside will fail.

• The speaker introduces methods for accessing private attributes through accessor (getter) and mutator (setter) methods, which will be covered in future lessons.

Method Accessibility

• Public methods such as "escrever" can be called directly on objects, while private methods cannot be accessed externally.

• Only public attributes and methods are accessible from outside the class; all others remain hidden to maintain encapsulation.

Real-world Analogy: Remote Control

• The speaker uses a remote control analogy to explain visibility: external components represent public access while internal components may need protection.

• This distinction helps clarify why certain parts of an object should remain inaccessible to users for security and integrity reasons.

Conclusion on Object Interaction

Understanding Visibility and Control in Programming

The Concept of Private Parts in Programming

• The discussion begins with the importance of privacy in programming, emphasizing that certain parts must remain private to maintain control and extend its duration. This is likened to a capsule that protects sensitive information.

• An example is provided using a chip that transmits infrared signals for television control. It highlights the necessity of restricting access to this chip while ensuring it remains accessible to the television for functionality.

• The speaker introduces the idea of "protected attributes," where only specific entities (like a remote control) can utilize certain methods or properties, reinforcing the concept of controlled visibility.

Moving from Theory to Practice

• The speaker clarifies that understanding visibility does not equate to complete comprehension; practice is essential for mastery.